Pertronix pointless ignition module

I was searching for some info on the Pertronix points substitute, and came across Bill’s opus in the 67 XR7 Build Thread?!

I’ll reproduce what Bill (xr7g428) wrote and then ask my question. Bill’s comments should be made into a sticky thread and future questions about Pertronix ignitors directed here. Bill could be a technical writer if his current day job ever falls through.

A drawing I made:

So here’s my question:

Why does Pertronix require/recommend the lower resistance coils (.6 ohm for the P-II and .3 ohm for the P-III)? Can they be used with the stock 1.5 ohm coil? What are effects/consequences?

How incredibly ironic. I just wrote almost the same story for Legendary Cougar Magazine, only not half as well. It does have pictures though.


  1. The .6 ohm coil when used with the inline resistance wire will get you to over 2 ohms and it will work pretty well. Keep in mind that with an XR-7 you are running all that current through a tach that is pretty old, and even under ideal conditions they are starting to fail. Eric Overton could write an entire thesis about what happens inside the molecular structure of old solder joints, but I will just put it this way: it ain’t pretty.

A lot of what we write on here is opinion, and my opinion is that you are better off putting money into a Rocketman 3 wire tach if you are trying to build a more robust ignition system. I see tach failure as a pretty predicatable event when you bump up the current feed.

  1. The .3 ohm coil can be switched by the P-III. But it will pull more current through the ignition switch than it was designed for. In that case you need to use an external relay, and both Rocketman and Pertronix offer these.

I really like the idea of the external relay, and I am doing an installation article on that next. I think it can be useful for both ignition and also electric choke.

OK… dumb this down a little… the lower ohm coil generates increased voltage, enabling a stronger spark at the plug - which is a good thing. But, it also increases the current drawn through the ignition switch, 45 year old wiring and, most critically, the tachometer if so equipped - which is in the strand-you-on-the-side-of-the-road category of potential bad things. These issues can be resolved with modifications such as adding a relay and three-wire tach. However, (despite what the application chart on Pertronix’s website suggests), the PII and PIII will operate just fine with a standard 1.5 ohm coil. Still, and regardless of any of this, one might consider a three-wire tach since the OEM tach is a weak link whether using points, Pertronix, OEM or high voltage coil.

Do I have this about right?

As you may recall, I had a P-II fail on me, so I’m a little leery about going back to it, and want to make sure I understand all the ins and outs.

So, steer clear of the pertronix?

Sent from my iPad using Tapatalk

You seem to have it right. The reason that they fail is that people try to take a short cut and use the 6 or so volt power at the coil.

True for the Petronix II, but the Petronix I is solid with the existing pink resistor wire. It is rare that it fails in that stock configuration, usually when the pink resistor wire is already faulty.

Most P1 failures were caused by having the key on with engine off.
I have never heard of a P1 working better with 12V, although Eric’s description of the switch makes sense.
The P2 on the other had seems to run ‘okay’ on 9-10 but wakes up with 12V.
I wouldn’t install a P3; if I want multiple spark or a rev limiter I will go MSD.
As a quick, easy, affordable points replacement it’s tough to beat a Pertronix.

I installed a Pertronix I in my Cat and had it running with the 6 volt resistor wire for a number of years but I finally got around to wiring in a relay to provide the ignitor 12 V and it performs like night and day! With 6 Volts, it ran a little rough when cold and had a slight hesistation when bringin` down the hammer. After wiring it with the 12 V, she starts and purrs and gitte ps and goes when I lay down the hammer.

BTW, I do carry a set of old points and a condensor in the glove box but I have never had to use them!

Coach Jack

Pertronix 1 is not good with less than about 9 volts. It won’t fail right away, but it doesn’t work properly.

Good to know.

Just my two cents, but the P3 distributor I have ran fine for almost a year (intalled before I got the car) off of the 6 volts and just last week gave me the same problem (stumble on fast/hard acceleration, then wanting to die at idle, then no idle, but fine startup). Will go to 12v and hope like hell it isn’t in complete failure.

It might actually be a good idea for Pertronix to put this on the instructions for their dizzies as well as point conversions. Would save a LOT of headaches and potential mad customers.

Pertronix might not be the best ignition in the world but lots of people use them, I hardly think they are a “pointless ignition module”, they have their place.

Robert - your pun radar needs re-calibration.

The instructions could be more clear about this, but they do mention the problem.

Many vehicles came equipped with ballast resistors or resistance wires. To
achieve optimum performance we recommend removal of these components.
Determine the proper wire length, and attach the provided terminals.
(Use a wire crimping tool to achieve an adequate connection).

I’ll have to check the cal label and get back with you…

As an inspector, do I need to document this non-conformance?

Just checked, Governor Christie eliminated the need for periodic re-calibration as a state cost-cutting measure. I was reminded of that this morning when the wheel fell off of my car on the way to work, he cut the state vehicle inspection back to little more than an emissions check…

He assumed car guys could check their own wheels. :slight_smile:

You know what happens when you assume.