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INFO: 72 - 79 Gauge Clusters and Wiring

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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
73 GTS 351 CJ
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-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
73 GTS 351 CJ
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 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

1972 Ford GTS Sportsroof - Survivor, One Family car
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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
JOHN
74 GRAN TORINO S&H CLONE
74 CORVETTE COUPE 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
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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
73 GTS 351 CJ
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 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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Post Options Post Options   Thanks (0) Thanks(0)   Quote Power Surge Quote  Post ReplyReply Direct Link To This Post Posted: 15-October-2017 at 1:46PM
Originally posted by 72torino... 72torino... wrote:

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

When you say another wire....do you mean off the tach? Does your tach have two wires or three coming off it? 

Your circuit should be like this.... 

Ign swtich>--resistor wire--red/green wire into tach>--TACH--<red/green wire out of tach---- positive coil post.


Sal Mennella
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75 Cougar XR7
73 Ranchero - 5.0 Coyote swap - in progress
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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 1:54PM
I have a two wire tach. One side says IGN the other side says coil. If the wiring is the way you have it described I don’t have it correct. I’ll work on that tomorrow and report back. Very thankful for your help. Wiring can be quite frustrating
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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 2:44PM
Alright, here is what I wound up doing...

I used the underhood key on power wire (I think it was originally the optional idle solenoid power), hooked to the + coil post. I put the red wire from the dist to the + coil post. I then used the "I" terminal on the starter solenoid for crank power, and hooked it to the + coil post. 

The original ignition/tach wire from the car is now disconnected from the coil. 

The car starts perfect and runs great. Just no tach operation now. I will have to send the tach out to be converted at some point. 
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 californiajohnny Quote  Post ReplyReply Direct Link To This Post Posted: 15-October-2017 at 6:57PM
Originally posted by 72torino... 72torino... wrote:

I have a two wire tach. One side says IGN the other side says coil. If the wiring is the way you have it described I don’t have it correct. I’ll work on that tomorrow and report back. Very thankful for your help. Wiring can be quite frustrating
you need to cut the wire outside of the firewall running to the + of the coil, connect a wire to the cut end coming from the firewall to the tach like in the diagram, the other wire from the tach will connect to the other end of the wire you cut running to the + of the coil! the "X" is showing the cut in the original wire... basically the coil power is running inline through the tach!!! ign will connect to the firewall side of that cut wire the coil one of the tach will go to the remaining wire to the coil (check that you don't have the tach wires reversed???)


Edited by californiajohnny - 15-October-2017 at 7:05PM
JOHN
74 GRAN TORINO S&H CLONE
74 CORVETTE COUPE CUSTOM
90 S10 BLAZER 4X4 LIFTED
77 CELICA CUSTOM
75 V8 MONZA SUPERCHARGED
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75 VEGA V6 5 SPD
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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 7:02PM
if it's wired like this and the tach dies usually the engine won't run! i say usually!!! i converted my dash and the car ran but the tach didn't work! i replaced the tach with another one and it works Shocked
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74 GRAN TORINO S&H CLONE
74 CORVETTE COUPE 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
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Post Options Post Options   Thanks (0) Thanks(0)   Quote BackInBlack Quote  Post ReplyReply Direct Link To This Post Posted: 16-October-2017 at 12:08AM
An alternative approach to that tach wiring is simple bypass the wire at the Tach connector in the harness under the dash.  This cuts the tach out of the circuit.  In place of the 2 wires passing through the connector 1 of the wires can be "repurposed" as a voltage tach sensor wire.   This requires replacing the tach with a new style voltage tach.   I have the tach output of my MSD box integrated into the engine wiring harness now.   All the extra ignition control signals, including the tach from the MSD box (6AL-2 programmable), is a separate harness that follows the old harness in the engine bay and passes through the firewall through the hole where the old EGR control harness passed through.   I removed all the EGR harness.  (72 doesn't have this EGR circuit and will require mods to the firewall.)

This how I'm handling the tach in the near future.

I have a decal kit to redo the face of the tach to convert to 8K and plan to send my tach to rocketman in the near future for the conversion.  He tests and calibrates the tach.   I called and spoke to him about his conversion and the test equipment he uses.     

Pic of this conversion

Diagram of teh circuit described

Hope this helps.


Edited by BackInBlack - 16-October-2017 at 12:50PM
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 72FordGTS Quote  Post ReplyReply Direct Link To This Post Posted: 16-October-2017 at 12:10PM
Originally posted by Power Surge Power Surge wrote:

[

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
 
I am not too familiar with the RTR MSD distributors, but it sounds like you may correct about the direct connection.  I did a lot of research and bottom line is that it's really tough and a ton of hassle to keep the factory tach.  It's just so much easier to convert it to a three wire voltage reading tach, since it's connected in parallel and has no effect on the ignition whatsoever. 
 
And even if you can get a in series Amp sensing tach to work properly, how long before that 45 year old instrument craps out?  At least with the conversion you get a modern accurate tach movement.  I know John mentioned the Tach adaptors too, but I read mixed reviews on them working properly. 
 
It costs a few bucks, but I stand by that the Tach conversion is the best and easiest way to have a non-stock ignition and have a factory appearing tach that is reliable and accurate.  It sounds like the bypass of the tach is the best thing until you can get it converted.
Vince

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Post Options Post Options   Thanks (0) Thanks(0)   Quote 72torino... Quote  Post ReplyReply Direct Link To This Post Posted: 22-October-2017 at 6:49AM
Just wanted to thank you all for the assistance I was able to get my tach working the other night.

This website has been a great resource
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