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INFO: 72 - 79 Gauge Clusters and Wiring

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Power Surge Quote  Post ReplyReply Direct Link To This Post Posted: 23-July-2017 at 4:11PM
So back to this topic and my previous question....  

I've got the sport cluster out of the 73 Ranchero. Along with the harness on the back. 

I know there is also a harness that goes from the cluster to the firewall. Does this harness need to be swapped between a sport and non-sport car of the SAME year? Or do both cars have the same harness? 
Sal Mennella
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75 Cougar XR7
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Post Options Post Options   Thanks (0) Thanks(0)   Quote californiajohnny Quote  Post ReplyReply Direct Link To This Post Posted: 23-July-2017 at 5:39PM
there is a smaller harness that is for the amp and tach wiring?
JOHN
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Power Surge Quote  Post ReplyReply Direct Link To This Post Posted: 24-July-2017 at 2:52PM
This is the harness I'm asking about. Is this harness different between sport and non-sport of the same year? 


Sal Mennella
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75 Cougar XR7
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Post Options Post Options   Thanks (0) Thanks(0)   Quote MrSmog Quote  Post ReplyReply Direct Link To This Post Posted: 24-July-2017 at 3:14PM
ok here's another question to probably muck things up. are all the engine harnesses for the sport cluster the same as in 302/351w, 351c/400,429/460? I would think they aren't but not sure. I may swap my sport cluster off my 351cj/4spd car into the 302/c4 car. Eventually i'll swap the 351cj/4 spd into this car, so i'd rather not cut and hack the engine harness up if possible.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote californiajohnny Quote  Post ReplyReply Direct Link To This Post Posted: 24-July-2017 at 4:20PM
the non sports won't have that harness! it's wrapped into the whole under dash harness BTW
most should be the same except maybe the short engine harness(coil/ oil/ temp) maybe be different for the BB's but that short harness plugs into the main under hood harness by the wiper motor
JOHN
74 GRAN TORINO S&H CLONE
74 VETTE CUSTOM
90 S10 BLAZER 4X4 LIFTED
77 CELICA CUSTOM
75 V8 MONZA SUPERCHARGED
79 COURIER VERT. SLAMMED
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Power Surge Quote  Post ReplyReply Direct Link To This Post Posted: 12-August-2017 at 3:17PM
Does anyone have a picture of what this looks like on an original 72/73 car? I am swapping the sport cluster over between two 73 cars using the factory parts and I don't see anything like this on the solenoid end of the sport cluster engine harness....






Sal Mennella
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75 Cougar XR7
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Rockatansky Quote  Post ReplyReply Direct Link To This Post Posted: 12-August-2017 at 3:32PM
IIRC the shunt is folded & looped into the dash harness
 
the pic may just be short for simplicity
72 GT Ute
   
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Power Surge Quote  Post ReplyReply Direct Link To This Post Posted: 12-August-2017 at 3:55PM
Originally posted by Rockatansky Rockatansky wrote:

IIRC the shunt is folded & looped into the dash harness
 
the pic may just be short for simplicity

Here's my problem...  look at the picture below. That's the end of the harness off the Ranchero, which is a factory sport cluster car. If you look at it, you'll see a fusible link going to the power side of the starter solenoid. And you'll see a heavy power wire going to the junction block. That's how it came off the Ranchero. Something else obviously went to the junction block, but I'm not sure what, since the Ranchero has been apart for a while now.


The only thing different on this harness from the original non-sport harness is that heavy wire going to the junction block. 

I thought maybe that the power wire from the alternator goes to the junction block (it was originally on the power side of the solenoid), because there's nothing else I can see to go there to give that power, so that's how I hooked it up. 

With it hooked up like this, the car DOES charge, but the ammeter doesn't seem to work, as it doesn't move at all. 



Edited by Power Surge - 12-August-2017 at 3:58PM
Sal Mennella
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75 Cougar XR7
73 Ranchero - 5.0 Coyote swap - in progress
Past Torinos - 72 Gran Torino, 75 Gran Torino, 75 Elite
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Power Surge Quote  Post ReplyReply Direct Link To This Post Posted: 13-August-2017 at 2:36PM
I found the factory wiring schematics, and according to what I am seeing, I do have the car wired properly. I think I may have damaged my ammeter, as I did snag the needle when I was cleaning the gauge face. It does still spring back and forth, but that doesn't mean I didn't tweak something in the gauge. I wish I could verify for sure though, because I want to do a write up for here. 
Sal Mennella
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75 Cougar XR7
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Post Options Post Options   Thanks (0) Thanks(0)   Quote californiajohnny Quote  Post ReplyReply Direct Link To This Post Posted: 13-August-2017 at 6:16PM
from what i've seen on the sport cars i've parted... that heavy wire to the junction block is the heavy shunt wire
JOHN
74 GRAN TORINO S&H CLONE
74 VETTE CUSTOM
90 S10 BLAZER 4X4 LIFTED
77 CELICA CUSTOM
75 V8 MONZA SUPERCHARGED
79 COURIER VERT. SLAMMED
75 VEGA V6 5 SPD
70 CHEV C10 P/U
68 MUSTANG FB CONVERSION
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Post Options Post Options   Thanks (0) Thanks(0)   Quote californiajohnny Quote  Post ReplyReply Direct Link To This Post Posted: 13-August-2017 at 6:28PM
sal, if you look at the above diagram... basically the ammeter and shunt go in between the main power wire from the alternator and the positive of the battery, so it flows through the gauge, the heavy shunt is to bypass some of the amps flowing through the gauge so it reads correctly
JOHN
74 GRAN TORINO S&H CLONE
74 VETTE CUSTOM
90 S10 BLAZER 4X4 LIFTED
77 CELICA CUSTOM
75 V8 MONZA SUPERCHARGED
79 COURIER VERT. SLAMMED
75 VEGA V6 5 SPD
70 CHEV C10 P/U
68 MUSTANG FB CONVERSION
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Post Options Post Options   Thanks (0) Thanks(0)   Quote BackInBlack Quote  Post ReplyReply Direct Link To This Post Posted: 14-August-2017 at 12:19AM
I just rewired the engine harness and had the wrap removed to the washer motor. That big 4awg black wire w red stripe is the main power lead for the fuse blocks.

I didn't find 2 fuse links shown in the diagram, only one.   The power lead should be connected to the battery side of solenoid.   Based on current loading...I'm not sure why it was connected to the junction post.   That means the current runs through that 8 awg wire to the post then onto that 4 awg wire.  

Mine had a soft flexible yellow wire which is the fuse link connected to the separate terminal. There is also a jumper wire connecting the battery side of selenoid to the terminal stud.

Edit:
I dont trust the fuse links of these old designs.  if the is a short somewhere in the circuit it can take down other circuits or even melt wire and cause a harness fire. These are very dependent on the use of fuse links in the circuit.  I'm surprise ford just wrapped them up in the harness with the rest of the wiring.  Some Chrysler stuff I've seen...I remembered they were isolated from the harness such that when they burned out it wouldn't damage the harness.   Maybe I'm paranoid...it lasted 40yrs...but will it last another 10+.  I'm not taking that chance.

I'm in the process of converting my tach to a voltage type and converting the ampmeter to a voltmeter.

If you're going for an oem restoration you might want to inspect/test the multiple fuse links and replace them


Where does that black wire with yellow crimp terminal go?



Edited by BackInBlack - 14-August-2017 at 7:00AM
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Post Options Post Options   Thanks (1) Thanks(1)   Quote Power Surge Quote  Post ReplyReply Direct Link To This Post Posted: 14-August-2017 at 11:37AM
Originally posted by BackInBlack BackInBlack wrote:

I just rewired the engine harness and had the wrap removed to the washer motor. That big 4awg black wire w red stripe is the main power lead for the fuse blocks.

I didn't find 2 fuse links shown in the diagram, only one.   The power lead should be connected to the battery side of solenoid.   Based on current loading...I'm not sure why it was connected to the junction post.   That means the current runs through that 8 awg wire to the post then onto that 4 awg wire.  

Mine had a soft flexible yellow wire which is the fuse link connected to the separate terminal. There is also a jumper wire connecting the battery side of selenoid to the terminal stud.

Edit:
I dont trust the fuse links of these old designs.  if the is a short somewhere in the circuit it can take down other circuits or even melt wire and cause a harness fire. These are very dependent on the use of fuse links in the circuit.  I'm surprise ford just wrapped them up in the harness with the rest of the wiring.  Some Chrysler stuff I've seen...I remembered they were isolated from the harness such that when they burned out it wouldn't damage the harness.   Maybe I'm paranoid...it lasted 40yrs...but will it last another 10+.  I'm not taking that chance.

I'm in the process of converting my tach to a voltage type and converting the ampmeter to a voltmeter.

If you're going for an oem restoration you might want to inspect/test the multiple fuse links and replace them


Where does that black wire with yellow crimp terminal go?


John (and CalJohnny), this is how the Ford schematic shows it (for a sport cluster car)....

You have the starter solenoid, and you have the junction block.

There is a heavy black and orange wire coming off the alternator, and that goes to the junction block.

There is a heavy black and orange wire coming from the fuse block harness. This also goes to the junction block. 

There is a yellow wire ending in a fusible link coming from the fuse block harness, that goes to the battery side of the starter solenoid. 

By running the alternator output to the junction block, you're feeding power to the car right from the alternator, and it's NOT going through the starter solenoid. Basically, the power from the battery just runs the starter. Once the car is running, the current needed to run the car is coming directly from the alternator output (which is very smart). That heavy black/orange wire in the fuse block harness turns into two smaller yellow wires, which then go into the fuse block to feed power to the ignition switch.

As far as the ammeter wiring goes... You have a yellow wire and a red/orange wire coming from the ammeter harness. The yellow wire splices into the heavy black/orange wire, which goes to the junction block. The red/orange wire turns into the yellow fusible link, which goes to the starter solenoid. IN BETWEEN where the red/orange wire turns to the fusible link, and where the yellow ammeter wire splices into the heavy black/orange, there is a connecting shunt wire that attaches to both wires. 

As John stated, I also do not see a second fusible link. Maybe you need to have one when you aren't using a factory sport harness. 

So from what I am seeing, the car takes it's main running power from the alternator, and then senses that amperage difference to the battery side (at the solenoid). 

A few other notes. A STANDARD cluster car, does NOT have the heavy black/orange wire in the fuse block harness. It has a single yellow fusible link attached to the battery side of the starter solenoid. That single wire splits into the two yellow power wires back to the fuse block. The heavy black/orange wire on the alternator, turns into a black fusible link and also goes to the battery side of the starter solenoid. So on a standard cluster car, the alternator wire and fuse harness wire just meet on the starter solenoid terminal. 

Now some people may have a jumper or circuit breaker, going from the starter solenoid to the junction block. These have nothing to do with the gauges or charging. These jumpers/breakers are used on cars that have other options that require power feed (power windows, etc). 

That's what I've come up with so far Big smile
Sal Mennella
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75 Cougar XR7
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Post Options Post Options   Thanks (0) Thanks(0)   Quote BackInBlack Quote  Post ReplyReply Direct Link To This Post Posted: 14-August-2017 at 12:35PM
You are 100% correct to the best of my memory regarding the OEM wiring.  The fuse link connected to battery side of starter selenoid ... black/org stripe wire and alternator output connected to the junction block.

Your comments fired a synapse.  I'm sorry I got on a tangent and didnt' really answer your question.   I was mistakenly discussing the changes I made to support new 1-wire alternator where the regulator is integrated.   It basically connects directly to the battery.  I move that black wire with orange stripe to the battery side of the selenoid since the alternator connects directly to hte battery.  


I would be surprised if the harness for the standard gauges didn't have the "black with red/orange stripe" wire to the fuse block.  The reason i say this is because of the current handling of that wire in general.  Obviously the heavy cable is required to the fuse block to distribute power.   The lights have power whether the engine is on or off and it gets power through that heavy cable.   Although...ford does some crazy things sometimes.   Would be kinda typical.


Refresh my memory...given the connection of the alternator and  black wire with orange stripe connect to the junction block.  Where is the battery connection to the alternator?   I'm thinking that it was through the voltage regulator to the battery side of the starter solenoid.

Kinda sounds like the fuselink wire is actually the wire carrying the current for the fuse block...I will look at my wiring again and get back to you ....this isn't making sense...this must be the fuselink that is the actual "main" fuse for the fuse block.   This is why there is 2 fuse links...one for the ampmeter and the other for fusing the connection to the fuse block.

 
This has me rethinking the 1-wire alternator setup.   I had forgotten the OEM wiring because my car was torn apart so long and I didn't take notes.   I'm thinking that I may need a relay to shut off power to the black wire with orange stripe when the engine isn't running.   Mmmmm thinking...  I need to get hold of the car schematics.



Edited by BackInBlack - 14-August-2017 at 1:01PM
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Power Surge Quote  Post ReplyReply Direct Link To This Post Posted: 14-August-2017 at 1:23PM
Originally posted by BackInBlack BackInBlack wrote:


I would be surprised if the harness for the standard gauges didn't have the "black with red/orange stripe" wire to the fuse block.  The reason i say this is because of the current handling of that wire in general.  Obviously the heavy cable is required to the fuse block to distribute power.   The lights have power whether the engine is on or off and it gets power through that heavy cable.   Although...ford does some crazy things sometimes.   Would be kinda typical.

Well think about this...on the standard dash car, the alternator heavy cable (which is the same 8 gauge black/orange cable) just turns into a 14 gauge fusible link, and a small yellow wire that goes to the voltage regulator. That fusible link goes to the starter solenoid. That 14 gauge wire is supplying all the power to the car from the alternator. So it's not surprising that they are going from that main 8 gauge cable to two smaller gauge yellow feed wires to the ignition switch. Also keep in mind that these cars stock didn't really have much electrical demand. 

Originally posted by BackInBlack BackInBlack wrote:

Refresh my memory...given the connection of the alternator and  black wire with orange stripe connect to the junction block.  Where is the battery connection to the alternator?   I'm thinking that it was through the voltage regulator to the battery side of the starter solenoid.

The alternator generates it own voltage. It does not need the battery. You could disconnect the battery after the car is running, and it will still run. The battery is mainly there to start the car. The yellow wire that splits off the black/orange cable coming from the alternator feeds power to the voltage regulator. 

Originally posted by BackInBlack BackInBlack wrote:

Kinda sounds like the fuselink wire is actually the wire carrying the current for the fuse block...I will look at my wiring again and get back to you ....this isn't making sense...this must be the fuselink that is the actual "main" fuse for the fuse block.   This is why there is 2 fuse links...one for the ampmeter and the other for fusing the connection to the fuse block.

On a standard dash car, the main power to the car IS going through the fusible link. On a sport dash car, the main power is going through the black/orange cable. On a sport dash car, I only see ONE fusible link. The yellow one coming off the starter solenoid. On a standard dash car, there is a second fusible link coming from the alternator. 


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75 Cougar XR7
73 Ranchero - 5.0 Coyote swap - in progress
Past Torinos - 72 Gran Torino, 75 Gran Torino, 75 Elite
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Post Options Post Options   Thanks (0) Thanks(0)   Quote BackInBlack Quote  Post ReplyReply Direct Link To This Post Posted: 14-August-2017 at 3:35PM
"The alternator generates it own voltage. It does not need the battery. You could disconnect the battery after the car is running, and it will still run. The battery is mainly there to start the car. The yellow wire that splits off the black/orange cable coming from the alternator feeds power to the voltage regulator. "

Agreed except the battery needs the alternator to charge.  The alternator output is a rectified output not a regulated DC voltage.  The output of the alternator should go through the regulator before getting distributed to charge the battery.   I was looking for how it was connected to the battery because I changed my wiring and can't remember the original connection.   Also, isn't the regulated 12Vbatt also distributed to the fuse block, not the unregulated output of the alternator?


"On a standard dash car, the main power to the car IS going through the fusible link. On a sport dash car, the main power is going through the black/orange cable. On a sport dash car, I only see ONE fusible link. The yellow one coming off the starter solenoid. On a standard dash car, there is a second fusible link coming from the alternator. "

I missed the info regarding the black/orange stripe wire getting spliced to the heavy yellow going into the fuse block.  Thanks for clarifying that.   I'm still thinking that the ford engineers would have put a "fuse" between the battery/alternator source and the fuse block.   I think we (or I) are missing a fuse link somewhere.   I believe there is a fuse link in the ampmeter circuit loop, a fuse link in the tach circuit loop (aka ignition source to coil), and a fuse link between the 12V power and the fuse block.  

I bet we are missing a fuse link or at least I am.


edit: I just found this...
I suspect the circuit is like this one.



Edited by BackInBlack - 14-August-2017 at 3:51PM
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Post Options Post Options   Thanks (0) Thanks(0)   Quote BackInBlack Quote  Post ReplyReply Direct Link To This Post Posted: 15-August-2017 at 12:22PM
I can't find any reference that shows a fuse link between the fuse block and the alternator.   Kinda bothers me that there isn't a fuse link for the output of the alternator feeding that black/orange stripe wire.   Any chance you have the harness unwrapped for inspection?  

After digging deeper into the design of the charging system...i never really appreciated simple elegance of the design.   However, I can also see why there is so much noise in the dash harness and why it couples into audio systems.   Its hardly a conditioned DC voltage nor really regulated, but it works.

I cannot find teh schematic of these years cars online.  I will have to buy a manual.  Anyway...I think you solved your own problem.    Working this exercise helped me double check my changes.  
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Power Surge Quote  Post ReplyReply Direct Link To This Post Posted: 15-August-2017 at 1:06PM
Originally posted by BackInBlack BackInBlack wrote:

I can't find any reference that shows a fuse link between the fuse block and the alternator.   Kinda bothers me that there isn't a fuse link for the output of the alternator feeding that black/orange stripe wire.   Any chance you have the harness unwrapped for inspection?  

After digging deeper into the design of the charging system...i never really appreciated simple elegance of the design.   However, I can also see why there is so much noise in the dash harness and why it couples into audio systems.   Its hardly a conditioned DC voltage nor really regulated, but it works.

I cannot find teh schematic of these years cars online.  I will have to buy a manual.  Anyway...I think you solved your own problem.    Working this exercise helped me double check my changes.  

There are definitely fusible links there. A standard cluster car has two....  one is right on the feed wire from the alternator to the starter solenoid (black 14 ga), and the other is the yellow 14 ga also attached to the starter solenoid. That yellow one feeds the two yellow wires that power the car. 

On a sport cluster car, it has the yellow one off the starter solenoid. But looking at the schematic, that fusible link looks like all it protects is a short to ground in the ammeter wiring. The black/orange wire turns into the two yellow wires going into the car.... but the fusible link is just a splice off that leg, so you are correct..... there is no fusible link protection on a sport cluster car. 

It's funny you mention audio noise. I put a new radio in my car recently (a better working stock 73 am/fm). Since then, I have noticed heavy rpm noise through my speakers with the radio on, when there is a load on the car (i.e. lights at night). I've been trying to solve that one. 
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Past Torinos - 72 Gran Torino, 75 Gran Torino, 75 Elite
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Post Options Post Options   Thanks (0) Thanks(0)   Quote californiajohnny Quote  Post ReplyReply Direct Link To This Post Posted: 15-August-2017 at 1:12PM
check you stereo grounds! it's called a ground loop that causes that.
 grounds for each component should be less than 18" but with this factory system using the common ground that may be hard
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74 VETTE CUSTOM
90 S10 BLAZER 4X4 LIFTED
77 CELICA CUSTOM
75 V8 MONZA SUPERCHARGED
79 COURIER VERT. SLAMMED
75 VEGA V6 5 SPD
70 CHEV C10 P/U
68 MUSTANG FB CONVERSION
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Power Surge Quote  Post ReplyReply Direct Link To This Post Posted: 15-August-2017 at 1:24PM
Originally posted by californiajohnny californiajohnny wrote:

check you stereo grounds! it's called a ground loop that causes that.
 grounds for each component should be less than 18" but with this factory system using the common ground that may be hard

Yeah, the radio case itself is the ground. I may pull the bracket and wire wheel the spots it bolts to. I was also thinking of adding an actual ground wire off the stud on the back to a better ground point. 

I have also been looking into grounding the speakers directly to the body, instead of sharing the common ground wire back to the radio. I think that would take the ground load off the radio.

BTW, BackinBlack....if you want to PM me your email, I can send you the pdf file for the 73 wiring schematics :)
Sal Mennella
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Post Options Post Options   Thanks (0) Thanks(0)   Quote abrewsterarchitect Quote  Post ReplyReply Direct Link To This Post Posted: 10-September-2017 at 2:38PM
thank you guys so much for your work. Really appreciate it!

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Power Surge Quote  Post ReplyReply Direct Link To This Post Posted: 14-October-2017 at 3:25PM
Here's another one hopefully someone might have some input on....

I installed a three wire ready to run electronic distributor today. Wires are coil +, coil -, and ground. 

I am using the factory positive voltage sensing sport cluster tach. 

They didn't seem to play well with each other. I think it has something to do with the tach fed voltage messing with the positive input to the electronic dist module. The car was hard to start (like the dist wasn't getting initial power), but once running it ran smooth. However the tach was jumping around and the car would randomly shut off, which seemed related to the tach jumping around. 

I found another plug not being used on the engine harness that had key power. However, it didn't maintain power in start. Since it was getting late, I just piggy backed it to the coil, this way I still had start power from the tach wire, but a clean 12v wire for the ignition module. 

The car runs great, but the tach now reads about half of actual rpms, and I'm not sure if I'm going to damage the tach like this. Plus I want the stock tach to work right. 

Any thoughts or ideas? I could run a new run/start power wire from the dash out to the engine bay, and run that to the module wire separated off the coil, but would prefer not to have to run an extra wire. 
Sal Mennella
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75 Cougar XR7
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Post Options Post Options   Thanks (0) Thanks(0)   Quote BackInBlack Quote  Post ReplyReply Direct Link To This Post Posted: 14-October-2017 at 11:52PM
I had the msd dizzy with the 3 wire interface that doesn't require an external ignition control module.   Worked fine no problems with the coil wired as stock per the instructions.

I've since added a 6al2 box and the dizzy uses the old coil positive wire as ignition on and I wired a separate ignition on to the 6al2 box. It al works fine.

Sounds like you may have a bad tach.   Did u try bypassing the tach by jumperingg across the 2 terminals on the tach connector?

Fyi...I'm converting my tach to a 8k tach which is voltage driven which takes the tach out of series with the ignition. So no more tach failure preventing the car from starting. There should be a thread somewhere regarding converting the tach

Edited by BackInBlack - 15-October-2017 at 12:34AM
-John
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Power Surge Quote  Post ReplyReply Direct Link To This Post Posted: 15-October-2017 at 2:30AM
Originally posted by BackInBlack BackInBlack wrote:

I had the msd dizzy with the 3 wire interface that doesn't require an external ignition control module.   Worked fine no problems with the coil wired as stock per the instructions.

I've since added a 6al2 box and the dizzy uses the old coil positive wire as ignition on and I wired a separate ignition on to the 6al2 box. It al works fine.

Sounds like you may have a bad tach.   Did u try bypassing the tach by jumperingg across the 2 terminals on the tach connector?

Fyi...I'm converting my tach to a 8k tach which is voltage driven which takes the tach out of series with the ignition. So no more tach failure preventing the car from starting. There should be a thread somewhere regarding converting the tach

Thanks John. I don't think it's a tach issue, as the tach has been working fine previously. 

I did however, do some more research last night and this morning, and I may have found the cause of the issue I was having with both the Pertronix and this new distributor....

Our cars use a resistor primary wire to the coil. This drops voltage to the coil to about 7-9 volts. Full 12 volts to a stock coil will burn it up. There is a bypass wire that's part of that circuit, that gives full voltage to the coil on START. The reason for this, is because during cranking voltage drops a few volts. So if you have 12.5 battery volts, that drops to about 10 during crank. Factor in the resistor wire and you'd only have about 6 volts to the coil during cranking. The by pass wire allows about 10 volts during cranking to the coil. And then back to 7-9 volts to the coil when running.

Now, I didn't realize this, but the Pertronix has a built in 1.5 ohm resistor. So combined with the factory resistor wire, I was basically running the Pertronix at like 5-6 volts. No wonder it wasn't working well, lol. 

As for the new distributor, running it through the factory primary wire is also running it at 7-9 volts, but the electronic module needs 12 volts running, and at least 10 volts on crank. 

What's the solution? Well, I could do away with the resistor wire, but 1) I just finished putting the entire restored dash and cluster together and don't want to pull it all apart again and 2) I am not sure how the factory tach would function on full voltage. 

So here is what I'm thinking....  I have a replacement starter solenoid that has the extra "I" terminal on it. That terminal supplies full voltage on cranking, which was used for this exact purpose on cars that did NOT have the bypass wire. And I already found a hot in run wire under the hood as well. So if I hook the hot in run wire and the "I" terminal feed to the positive wire for the ignition module, I will then have full battery voltage for the distributor. I can then leave the factory wire hooked to the coil, and the coil and tach can then operate on their original voltage circuit. 
Sal Mennella
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 72FordGTS Quote  Post ReplyReply Direct Link To This Post Posted: 15-October-2017 at 6:02AM
Sal,
you're on the right track. The positive feed (amp sensing) tach is very limiting and the easy solution is to have it converted by Tachman to a three wire voltage reading tach.  I did this on my car, and he does great work.
 
As you've figured out the problem is that the resistor wire reduces the voltage.  From what I have been able to find out, the factory tachs need that resistor wire, and will be damaged if you run a full 12 volts.  What I did when I still had the amp sensing tach, is I ran the tach to coil just like stock.  I ran an extra wire off the positive side of the coil to trigger a relay.  This relay would supply a full 12 volts to the pertronix.  So with this setup, I had the 8 volts going to the coil and tach, but the Pertronix got the full 12 volts.  You could probably run something similar with your setup as long as you don't need 12 volts to the coil.
 
If you need to use a 12 volt coil, I think the only real solution is to convert your tach to a three wire setup.  I am still just running a Petronix, but I will be converting to another setup soon, which is why I did my Tach first. 
 
Bottom line, convert the tach and it will make life far easier.
Vince

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Post Options Post Options   Thanks (0) Thanks(0)   Quote californiajohnny Quote  Post ReplyReply Direct Link To This Post Posted: 15-October-2017 at 7:10AM
IIRC the later cars had a 3 wire tach?
 IDK what i did on my car but i don't remember changing the resistance wirebut i did tap into it after the firewall for the tach, it all works! later thinking about this i checked voltage at the coil and have 11.8v so IDK???? but it all works!
 at first i added a short wire from the positive side of the coil to the stock 2bbl choke Confused that was stupid on my part... made the tach read incorrect, so i just unplugged that wire from the choke...tach was reading fine well driving down the road that wire touched the valve cover unbenounced to be and killed the engine ShockedAngryConfused figuring the 40 year old tach died Angry after 20 mins of trying the bypass the tach in the middle of the road BTW! then i see that wire grounding out Censored bent the wire so it can't touch boom car fires right up Clap drove home, got a wrech and removed that stupid wire and promptly threw it across the street into the woods never to be found again!!!!Angry
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Power Surge Quote  Post ReplyReply Direct Link To This Post Posted: 15-October-2017 at 9:25AM
Originally posted by 72FordGTS 72FordGTS wrote:

Sal,
you're on the right track. The positive feed (amp sensing) tach is very limiting and the easy solution is to have it converted by Tachman to a three wire voltage reading tach.  I did this on my car, and he does great work.
 
As you've figured out the problem is that the resistor wire reduces the voltage.  From what I have been able to find out, the factory tachs need that resistor wire, and will be damaged if you run a full 12 volts.  What I did when I still had the amp sensing tach, is I ran the tach to coil just like stock.  I ran an extra wire off the positive side of the coil to trigger a relay.  This relay would supply a full 12 volts to the pertronix.  So with this setup, I had the 8 volts going to the coil and tach, but the Pertronix got the full 12 volts.  You could probably run something similar with your setup as long as you don't need 12 volts to the coil.
 
If you need to use a 12 volt coil, I think the only real solution is to convert your tach to a three wire setup.  I am still just running a Petronix, but I will be converting to another setup soon, which is why I did my Tach first. 
 
Bottom line, convert the tach and it will make life far easier.

My circuit didn't work... not sure why... on paper it should have worked. 

I'm going to try your relay trick next....

Edit -   Well I tried the relay route (which in reality is the same thing as my previous idea just with a relay), and it did not work.

This distributor just won't work properly unless the positive wire is hooked directly to the coil. I am guessing the electronic module must need to sense both sides of the coil to work properly. It will fire on crank, but not stay running after that, if the positive wire to the dist has it's own separate power. But hook that wire to the positive coil, and it works fine. 

I guess at this point, I'll just have to bypass the factory tach and have it converted at a later date. Cry


Edited by Power Surge - 15-October-2017 at 10:48AM
Sal Mennella
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 72torino... Quote  Post ReplyReply Direct Link To This Post Posted: 15-October-2017 at 12:25PM
Question, trying to put a 74 sport cluster into a standard 72 cluster car. Cannot get the tach to work, I believe I have followed the wiring diagram on page 1. And I can take a VOM and get continuity between the wire at the coil and both the red/green stripe and red/ blue dot wire going into the back of the cluster on the IGN and coil areas.

Am I doing something wrong? Is there a way the tach could be bad.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Power Surge Quote  Post ReplyReply Direct Link To This Post Posted: 15-October-2017 at 12:49PM
Originally posted by 72torino... 72torino... wrote:

Question, trying to put a 74 sport cluster into a standard 72 cluster car. Cannot get the tach to work, I believe I have followed the wiring diagram on page 1. And I can take a VOM and get continuity between the wire at the coil and both the red/green stripe and red/ blue dot wire going into the back of the cluster on the IGN and coil areas.

Am I doing something wrong? Is there a way the tach could be bad.

Is it a two wire tach? If so, what you need to do is cut the red/green wire going to the POSITIVE of the coil, just outside the firewall in the engine bay. Then you run the two wires of the tach in SERIES, with the wire you just cut. 
Sal Mennella
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 72torino... Quote  Post ReplyReply Direct Link To This Post Posted: 15-October-2017 at 1:31PM
I believe I have that, I have a splice with the red green wire and off of it I have two wires running to the tach and then another that goes to he ignition switch I believe?

Is there a way to see if my tach is not operating properly
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