# Pertronix 12V Source on 70 GTO



## GoatBawb (Dec 18, 2016)

I am about to drop in my new Pertronix distributor and Flamethrower coil this weekend in my 1970. Apparently I have a resistor wire to my positive coil; I'm only seeing 6-8 volts there. Anybody got a good idea of where to tap into 12V? According to my wiring diagram, there is a yellow wire off the ignition switch that feeds the coil resistor wire. Would this be a good spot? I think I found the wire last night under the dash, but my 50-year old eyes and back don't work so well under the dash anymore. Any ideas are much appreciated.

And at the risk of heresy, what if I just use the resistor wire that's there? Will it hurt anything or reduce performance?


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## Shake-N-Bake (Jun 16, 2015)

You need 12 volts for the electronic ignition to function properly.
Does your car have the idle stop solenoid on the carb? If so, that should have 12v when key is on. You would need to verify that it has 12v when cranking though....if not, then it won't help you much. 

If the above idea isn't feasible there are a number of other options. The 6-8 volt wire could be used to signal a relay that would then power the electronic ignition. The switched voltage could come from the horn relay (which should have power full time, even while cranking).

Hope this helps.


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## RT-1 (Mar 21, 2012)

All you have to do is follow the coil wire back in the harness. That will require untaping quite a few wires. It will be obvious where the resister wire starts. Cut it out and solder a new wire at that point and run it to the coil. Alternatively, you can use the 8 volts to activate a Bosch relay to drive voltage straight from the battery.


Sent from my iPad using Tapatalk


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## BearGFR (Aug 25, 2008)

Easiest solution: Cut nothing, change nothing on the existing harness. Instead visit your local convenient parts store and buy yourself a generic headlight relay. Mount it at a convenient location on the firewall near your distributor. Disconnect what used to be the coil wire from the coil and use it instead to trigger the relay. (Coil wire goes to the + terminal on the energizing circuit, connect the - terminal on the energizing circuit to ground). Wire the contact side of the relay directly to the battery (through an appropriate inline fuse of course) and from thence (always wanted to use that word, thence) to your ignition. Done. Now you have a full 12v to your new ignition and you didn't have to butcher your factory wiring harness or stand on your head trying to trace wires to get it.

Start to finish, if it takes you more than an hour to do, something's wrong.

Bear


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## GoatBawb (Dec 18, 2016)

Thanks for the advice everyone. Actually after posting this, I checked the voltage while cranking and running, and had 12V in each case. So the 8V was only with the key on and not running. I dropped it in and it runs like a top. Al the hesitation I had when accelerating is gone. So I would recommend the Pertronix for anyone thinking about it.


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## rheckman (Aug 28, 2018)

BearGFR said:


> Easiest solution: Cut nothing, change nothing on the existing harness. Instead visit your local convenient parts store and buy yourself a generic headlight relay. Mount it at a convenient location on the firewall near your distributor. Disconnect what used to be the coil wire from the coil and use it instead to trigger the relay. (Coil wire goes to the + terminal on the energizing circuit, connect the - terminal on the energizing circuit to ground). Wire the contact side of the relay directly to the battery (through an appropriate inline fuse of course) and from thence (always wanted to use that word, thence) to your ignition. Done. Now you have a full 12v to your new ignition and you didn't have to butcher your factory wiring harness or stand on your head trying to trace wires to get it.
> 
> Start to finish, if it takes you more than an hour to do, something's wrong.
> 
> Bear


Bear,
When you say thence to ignition is it from the 4th terminal on the relay back to pos coil terminal,or from battery back to pos term on coil
?

Thanks 

Bob h


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## BearGFR (Aug 25, 2008)

A relay is nothing more than an electrically operated switch, right? The two terminals that make up the primary side energize a magnet that closes a contact to connect across the other two secondary terminals. So, in this case we use what used to be the ignition wire to supply power to the one of the primary terminals with the other primary terminal connected to ground. When power flows through this circuit because the ignition is in START or RUN, it closes the circuit on the secondary side --- which we connect to a solid 12v on one side and to the 12v connection on your ignition system, such as an HEI. Think of the relay as being a "remote" ignition switch that gets activated by the original ignition switch.

Bear


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## stich (Feb 15, 2016)

Not to rob the thread but on my 67, I bought an engine wiring harness for electronic ignition. My idea was that it would eliminate the resistor wire and run 12 volts to my new MSD disy. Was I right or will I have to do more? Thanks


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## PontiacJim (Dec 29, 2012)

The "relay" is a small black box having electrical tabs to which you secure your wires on to. Some have the corresponding plug in connection or you can buy it separately. If you want fancy, you can even get them fitted with a spade fuse. The basic relay comes in 30 & 40 amp ratings - 30 AMPs should work fine for you. The store bought relay switches should have the same terminal numbers I have cited in the text here.

You are simply using an on/off voltage supply wire which in this case will be your resistance wire that goes to the coil. (you could also use your ignition switch or ANY 12V source that becomes live when you turn on the key) to activate/open the relay.

Why? The resistance wire is just that, it provides resistance to drop the 12volts coming from the ignition switch down to 8volts so you do not burn the points on a points type distributor.

The HEI and most electronic distributors need the full 12volts and 8volts can create problems. So this is where the relay comes into play. To activate/open the relay switch, it only needs a low voltage source like 8volts. Once activated, the switch can then transfer/supply 12volts from an input source and then back out to the electrical item that requires the 12volts. 

You are connecting your resistance wire to the #86 terminal spade shown in the diagram which is hooked up to the ignition switch. This is what is going to activate/open the relay.

You will attach a 12volt power source to the #30 terminal spade. It can be directly from the battery or any other known 12volt power source that becomes live when you turn on the ignition key or is already live (a light source or horn wire would not work because these are not live nor have continuous 12volt power when the key is turned on). So #30 terminal is where the 12volts will come in from.

The #87 terminal spade is where the 12volts from your battery or other source will exit. It is on the #87 that you can then connect your distributor to (note in the diagram that this 12volt source can be used to hook into anything needing the full 12volts.)

And of course, the ground terminal which is self explanatory.

So let's review. The factory 8volt resistance wire coming from the key switch is ONLY being used to activate/open the relay switch. By throwing the internal switch, it opens the 12volt power that is coming into the #30 terminal and allows the 12volts to pass over to the #87 terminal and out to your coil so your coil will now have 12volts. When you turn off your key, the #86 terminal goes dead and the 12volts are shut off to your coil and engine stops.


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## MidnightAuto (May 28, 2018)

I’m planning on doing this mod at some point- here is my question- why can’t I skip the relay altogether? Find a 12v source on fuse box that works in start and run and just run that to coil?


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## PontiacJim (Dec 29, 2012)

MidnightAuto said:


> I’m planning on doing this mod at some point- here is my question- why can’t I skip the relay altogether? Find a 12v source on fuse box that works in start and run and just run that to coil?


You can. The relay is just an option and allows you to keep the resistor wire if you don't want to eliminate it and then use it as the source to power up the relay. If you sell the car or want to go back to the original points, easy enough to hook back up as original.

Another option is to wire directly off the ignition switch spade where the same wire/power source becomes your resistor wire.

I did a Pertronix electronic conversion and wired up a toggle switch right off the battery to the coil.

You can also get a new wiring harness that is wired for the 12 volts and has no resistor wire - if you were in need of replacing your wiring harness.

So you have a number of options, just depends on how you want to tackle it. :thumbsup:


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## MidnightAuto (May 28, 2018)

Got it. Thanks for feedback


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