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Voltage to Pertronix Coil

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bdaugette View Drop Down
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    Posted: 08-June-2019 at 12:51PM
SI My ignition was changed from points to Pertronix before I bought it.  I read that the old points had 6 volts to the coil, and the Pertonix needs 12.  Do I test this with the key off or on?  Do I test with the engine running?  Should there be a 12 V wire from the ignition, bypassing the resistor? 

The car runs, but I was watching a show that mentioned they were swapping points for Pertronix and had to run a wire.
Bill Daugette
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Post Options Post Options   Thanks (0) Thanks(0)   Quote californiajohnny Quote  Post ReplyReply Direct Link To This Post Posted: 08-June-2019 at 2:20PM
about 8 volts. the factory resister wire is from the ignition switch to the firewall IIRC, just replace it with a normal wire to get 12 volts
JOHN
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Post Options Post Options   Thanks (0) Thanks(0)   Quote californiajohnny Quote  Post ReplyReply Direct Link To This Post Posted: 08-June-2019 at 2:22PM
check the voltage at the coil with the key on positive terminal on the coil should be close to 12 volts if it reads 8 then you'll need to bypass that wire i have 11.8 at my HEI
JOHN
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Post Options Post Options   Thanks (0) Thanks(0)   Quote bdaugette Quote  Post ReplyReply Direct Link To This Post Posted: 08-June-2019 at 2:32PM
Thanks John.  I assume if it has 8 it will still run, but could be better...?
Bill Daugette
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Post Options Post Options   Thanks (0) Thanks(0)   Quote californiajohnny Quote  Post ReplyReply Direct Link To This Post Posted: 08-June-2019 at 3:05PM
possibly but may lag or cut out under heavy throttle??? i think the wire changes color from the resistor wire to the under hood wire...  i can look at a harness and see what color it is....
JOHN
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Rockatansky Quote  Post ReplyReply Direct Link To This Post Posted: 08-June-2019 at 3:09PM
what dash do you have Bill, factory tach?

also which Pertronix unit, I, II, or II ?

if standard cluster it'd easier to use the resisted coil supply to trigger a relay to supply battery voltage to the distributor but i'd talk to Pertronix tech before settling on a course of action, the original Pertronix I module is more delicate than the II and III

IIRC all versions of the Pertronix module should run fine using the resisted factory coil power supply, but again check with Pertronix
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 72FordGTS Quote  Post ReplyReply Direct Link To This Post Posted: 09-June-2019 at 12:13PM
Like John said, with the resistor wire you'll have about 8 volts.  This can power a Pertronix 1 module, but the instructions say 12 volts is preferred.  Lots of people install them without bypassing the resistor wire and they still seem to run - most of the time.
 
You really have two options. First is to bypass the resistor wire.  This will work, but if you are using a stock coil, it probably should be powered by 8 volts for it to last.  So you'd still have to run the original resisted ignition wire to the coil.  And if you have a factory Tach, you need to run the coil with 8 volts for it to read correctly and not burn out.
 
The second option, and easier IMO, is to run a relay.  This is what I did when I ran a Pertronix I.  Just run the ignition wire to the coil as normal.  Then add a second wire under the positive terminal (just a ring loop) and use that to trigger the Relay.  Get a 12 volt supply from your ignition solenoid and use that as your power source for your Pertronix.  You'll also need to install a fuse inline too.  Connect this to the Pertronix.  That way you will have a full 12 volts to the Pertronix, 8 volts a the coil, and a factory Tach will work perfectly. 
 
I believe Pertronix sells a relay kit, but I just bought one from a parts store and wired it myself.  If you need or want a basic wiring diagram, I can draw one up for you. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote bdaugette Quote  Post ReplyReply Direct Link To This Post Posted: 09-June-2019 at 12:28PM
I would like to see your wiring diagram.  I like the idea of the relay. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 72FordGTS Quote  Post ReplyReply Direct Link To This Post Posted: 09-June-2019 at 1:06PM
Originally posted by bdaugette bdaugette wrote:

I would like to see your wiring diagram.  I like the idea of the relay. 
 
Okay give me a few days and I make one up.  I don't have one handy at the moment.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote bdaugette Quote  Post ReplyReply Direct Link To This Post Posted: 09-June-2019 at 2:47PM
I have a factory tach, so I think I need the reduced voltage there, with the full 12 to the coil. I need to see which Pertronix I have.  It idles great, but not so great at higher rpms.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 72FordGTS Quote  Post ReplyReply Direct Link To This Post Posted: 10-June-2019 at 12:06PM
I found a diagram online that I was able to make a few changes to.  It's pretty simple to wire up.  I just mounted the relay on my inner fender near the solenoid.  If you have any questions let me know.
 
 
 
 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote bdaugette Quote  Post ReplyReply Direct Link To This Post Posted: 10-June-2019 at 12:44PM
Looks pretty simple, but the 12V feed couldn’t come from that side of the solenoid, right?  Seems like it would be hot to the coil all the time? I will look online now that I know something is out there.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote californiajohnny Quote  Post ReplyReply Direct Link To This Post Posted: 10-June-2019 at 2:01PM
yes it would be but with the relay open that power won't go anywhere, until the key is on to the coil that caused the relay to connect the 12v supply to the relay term. out to the pertronics mod Wink
JOHN
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 72FordGTS Quote  Post ReplyReply Direct Link To This Post Posted: 10-June-2019 at 2:22PM
Originally posted by bdaugette bdaugette wrote:

Looks pretty simple, but the 12V feed couldn’t come from that side of the solenoid, right?  Seems like it would be hot to the coil all the time? I will look online now that I know something is out there.
 
Like John said, this is correct.  The Relay is a basically a switch.  When your car ignition is turned out, power will be supplied to the coil (at the positive terminal). The new wire you run with ring terminal will then receive power, which will got to the relay and "switch it on".  This will turn on the other side, which will supply power to the ignition module.  Of course this all takes a split second.
 
I had Photoshop and modify an existing diagram. This is exactly how mine was wired when I had a Pertronix.  Worked fine for many years.
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