Factory Tach and Pertronix II.

Stanglover · Aug 25, 2024

I know this has been talked about a million times and there is so much under "search" to go through. I am sure someone posted on how to get a Pertronix II to work with a factory tach. There is an adaptor used on MSD distributors, but is there another way to get it to work. I have it in mind that someone did post on this and if so, can they repost it or PM me. I have a friend in need of replacing the points and want to run a PII. He is not wanting to send the tach out to be changed to negative.
Help appreciated.

Don C · Aug 25, 2024

No changes in the wiring are required. The PII works with and without the resistor. Leave the wire from the ignition switch (red with light green stripe) connected to the coil positive terminal. Connect the PII red wire to the positive terminal on the coil and the black wire to the negative terminal. The current sensing tachometer works the same as with a point ignition. Something like the MSD adapter is just needed when the wire from the ignition switch (and running through the tachometer) is not connected directly to the coil.

Stanglover · Aug 25, 2024

Don C said:
No changes in the wiring are required. The PII works with and without the resistor. Leave the wire from the ignition switch (red with light green stripe) connected to the coil positive terminal. Connect the PII red wire to the positive terminal on the coil and the black wire to the negative terminal. The current sensing tachometer works the same as with a point ignition. Something like the MSD adapter is just needed when the wire from the ignition switch (and running through the tachometer) is not connected directly to the coil.

Thank you Don, I'll pass that on to my friend.
I knew in the back of my mind that there was a way to use a PII with the factory tach.

SteveO_71 · Aug 26, 2024

Don C said:
No changes in the wiring are required. The PII works with and without the resistor. Leave the wire from the ignition switch (red with light green stripe) connected to the coil positive terminal. Connect the PII red wire to the positive terminal on the coil and the black wire to the negative terminal. The current sensing tachometer works the same as with a point ignition. Something like the MSD adapter is just needed when the wire from the ignition switch (and running through the tachometer) is not connected directly to the coil.

Wasnt there some issue with connecting the PII directly to the coil? Something about using the lower voltage that exists there. I recall reading conversations where people were saying to use a +12v connection to the PII. Or am I recalling this wrong and if so, please clarify.

Stanglover · Aug 26, 2024

SteveO_71 said:
Wasnt there some issue with connecting the PII directly to the coil? Something about using the lower voltage that exists there. I recall reading conversations where people were saying to use a +12v connection to the PII. Or am I recalling this wrong and if so, please clarify.

From what I remember, the PII can run on reduced voltage, but 12V is recommended.
A relay could be used to supply the 12V, but I'm not sure if this would work with the factory tach, which is the question.

Hemikiller · Aug 26, 2024

The Pertronix I or II can run on the resistor wire, but it can interfere with the proper tach reading. Best practice is to power the module by itself. You can use the Red w/Yellow hash wire originally for the anti-dieseling solenoid to power the Pertronix. That'll deliver a full 12V in Start and Run.

Stanglover · Aug 26, 2024

Hemikiller said:
The Pertronix I or II can run on the resistor wire, but it can interfere with the proper tach reading. Best practice is to power the module by itself. You can use the Red w/Yellow hash wire originally for the anti-dieseling solenoid to power the Pertronix. That'll deliver a full 12V in Start and Run.

Thank you Hemi, I'll pass that on to my friend.

rhigg1959 · Aug 26, 2024

I watched a video by Jeff from RestoMod on Youtube. His fix worked for mine, by buying a trailer wire extension and wiring it in line with the tach and splicing a wire from that harness to the coil. Worked perfect.

Stanglover · Aug 26, 2024

rhigg1959 said:
I watched a video by Jeff from RestoMod on Youtube. His fix worked for mine, by buying a trailer wire extension and wiring it in line with the tach and splicing a wire from that harness to the coil. Worked perfect.

Thanks, I'll check that out.

Barrysmach1 · Aug 26, 2024

Stanglover said:
I know this has been talked about a million times and there is so much under "search" to go through. I am sure someone posted on how to get a Pertronix II to work with a factory tach. There is an adaptor used on MSD distributors, but is there another way to get it to work. I have it in mind that someone did post on this and if so, can they repost it or PM me. I have a friend in need of replacing the points and want to run a PII. He is not wanting to send the tach out to be changed to negative.
Help appreciated.

no changes needed for pertronix or petronix 2 or any other single fire electronic ignition , now multi spark ignitions are a different story

Stanglover · Aug 26, 2024

Hemikiller said:
The Pertronix I or II can run on the resistor wire, but it can interfere with the proper tach reading. Best practice is to power the module by itself. You can use the Red w/Yellow hash wire originally for the anti-dieseling solenoid to power the Pertronix. That'll deliver a full 12V in Start and Run.

I may have mislead you. I did not mention this is on a 71. I looked at the wiring color diagram for this with tach and the only red with yellow hash powers the dual brake warning light #640. I do not see any reference to the anti-dieseling solenoid.
Were you referencing a later year?
As said, I'm trying to help a friend out so I can't look at my car for reference as it's a non tach car.
All help is much appreciated, thanks.

Hemikiller · Aug 27, 2024

Single wire in the engine bay harness with the white barrel connector shown by the Red arrow.

Stanglover · Aug 27, 2024

Hemikiller said:
Single wire in the engine bay harness with the white barrel connector shown by the Red arrow.

View attachment 92503

View attachment 92504

That's great info Hemi. Thanks.
This is all good info for others as well as I know this question has been asked (and answered) many times.

midlife · Aug 27, 2024

71 doesn't have that wire...

Hotstang · Aug 27, 2024

midlife said:
71 doesn't have that wire...

My 71 has that wire

Stanglover · Aug 27, 2024

Hotstang said:
My 71 has that wire

My 71 has a white plug, but I can't determine the color of the wire into it without opening the harness. As I'm not working on my car, I don't intend to do that. This white plug has a wire plugged into the other end, same thing.

Stanglover · Aug 27, 2024

midlife said:
71 doesn't have that wire...

This is on my car, not my friends. I have a white plug that is in use apparently. There is also a green plug not in use and a black one also not in use. I've not checked (yet) to see if these are 12V in RUN, but if one is, could that be used to power the PII? (Assuming my friends car is the same).
Sorry but I'm getting lost now and don't know what to advise.

EDIT: I took a look at my car, white plug. It does have 12V in the run position. When I bought this car, a PO had replaced the carb with a Holley 670. This has an electric choke and to be honest, I never bothered to find out where he powered it from. Well now I do. He used the white plug that has a red and something, could be yellow, wire. It has to be the 640 wire.
So with that figured out, I now know my friend can power the PII off that, unless of course it's in use for the solenoid as I don't know what carb he has, other than it's a 4V.

Hemikiller · Aug 27, 2024

midlife said:
71 doesn't have that wire...

That's a pic of my '71. It's also present on our 71 XR7 and is currently powering the HEI and choke.

Stanglover said:
This is on my car, not my friends. I have a white plug that is in use apparently. There is also a green plug not in use and a black one also not in use. I've not checked (yet) to see if these are 12V in RUN, but if one is, could that be used to power the PII? (Assuming my friends car is the same).
Sorry but I'm getting lost now and don't know what to advise.

The green female plug is for the automatic transmission shifter illumination, wire will be brown. Should only be hot when the lights are on.

Stanglover · Aug 27, 2024

Hemikiller said:
That's a pic of my '71. It's also present on our 71 XR7 and is currently powering the HEI and choke.

The green female plug is for the automatic transmission shifter illumination, wire will be brown. Should only be hot when the lights are on.

Thanks. Mine is manual, so likely no power. Useful to know anyway. Any idea what the black socket might be for? No power there as well.

Stanglover · Aug 27, 2024

Looking more closely at the diagrams and starting to understand them better, I see that the red/green stripe wire goes to one side of a 14A fuse, #16B or16A. The other side of that fuse is the red/yellow hash #640.
My question now is; if one powers a PII with this wire as suggested and the fuse blows, (one is stuck on the side of the road if no spare available or the driver is unaware of this fuse) is there a better option wire that is NOT fused, but still a full 12V in the RUN position?
Am I making this way too complicated?

Factory Tach and Pertronix II.

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