Pertronix Low Voltage Issue

From what I understand, the '68 E-type has a “resistor wire” versus the later “ballast resistor” in the ignition circuit. Following the installation of a Pertronix Igniter 2 and Flamethrower Coil recently I have been having problems with rough idle and an erratic tach ,among other things . I have gone through all the Pertronix troubleshooting tests and the problem appears to be eliminated when I connect the + lead of the coil directly to the + lead of the battery . The car starts and idles fine. Pertronix attribute the problem to a low voltage issue created by the “resistor wire” and their recommendation is to run a bypass wire around the resistor wire. Is it possible just to remove the resistor wire? I have no idea where it is located or what it looks like . If removal is not possible and a another wire must be run to the coil , I assume I would need to run it from the ignition switch which may be quite difficult. Are there any other options ? Seems like removing the resistor wire would be the easiest depending on where it’s located.
Thanks !
Don

I am not an expert on the 68 but I would be very surprised if it came with a resistor wire.

What color wire attaches to the positive terminal of the coil - is it white?

You can test the attributes of the coil you have by measuring the resistance across the low tension terminals (- & +). If it has low resistance (say 1.5 ohms) then it is expecting a resistor wire or ballast resistor. If it has higher resistance (say > 3 ohms) then no additional resistance is needed.

I expect it is the latter as I would think a lower resistance coil would fry the Pertronix (though I am also not a Pertronix expert).

I don’t know if a ‘68 E-type is wired similarly, but early Mustangs have an infamous “pink wire”, where the voltage to the points is 12V while starting, then drops to something like 6V after the engine is running…this causes all sorts of issues with drop-in electronic ignitions.

Some people choose to remove the pink wire entirely, but it’s a lot of work, because it’s well and truly buried in the harness.

Another option is to just run a parallel wire along the harness from a switched, 12V source.

Another option that I believe I saw a few people advocate is to have the low voltage wire operate a relay, and then take 12V directly from the battery.

Maybe try googling “Mustang pink wire” to get some more more ideas from the Vintage Mustang Forum…there are countless threads on that topic.

Cayo,The ballast resistor is not needed. The pickup and magnets do all the work.
That’s why when you went direct to the battery it was fine.
Eliminate the ballist, its not needed.
Your dropping the voltage instead of full current.
If you simply put the hot ballist wire to the coil with the positive red petronix and the black to negative on the coil you are done.
Make sense, if not pm me…
Remember the ballast was installed to not burn up the points with a spike and a condenser, that is now eliminated.
GTJOEY1314

I ran a parallel switched 12v on my BMW 2002tii and that worked. I do not know why this was not an issue on my 69 E.
Abe

From what I’ve read a resistor wire was installed on the ‘68 and in ‘69 they went to the ballast resistor. The low voltage problem is caused by the resistor wire and must be removed or by passed. The problem is , where is it located?
Thanks!

Thanks for your reply!

The red wire from the Pertronix and a black wire attach to the + terminal on the coil.

The black is ground…
Your white or hot from the key and red go together…
You will burn up that unit very fast…
hot from key / white should be at positive of coil with the red wire.
Black from petronix to the negative of coil your done…no ballast
good luck
gtjoey1314

Certainly not the case on my 69 S2. I believe later (perhaps 70) went with a ballasted system.

Hopefully you have a decent wiring diagram but if it is the multipage one from XKs then be careful as there is an error in the coil wiring (still shows it as positive ground).

You say you have a black wire to the coil - that may either a replacement or a braided white wire that has lost its outer cover.

Here is what I have;

Black wire from Pertronix to - on coil

Red wire from Pertronix to + on coil

Black wire from ?? to + on coil

Yellow wire with black stripe is unconnected

No white wire

The black wire to + on coil is definitely old judging by insulation on wire

Your almost there…
The Petronius wires to the coil are correct
Now take the yellow black wire and the other phantom black wire off of everything
Turn key on and off whilst using a test light on both
I have a feeling one of those are the hot to the key
Report back
The one that goes on with the key and off with the key is the hot lead
That wire goes to the positive side of the coil with the red wire
Easy test
Good luck

Looks like the black wire and it was on the + terminal of the coil.

But again when the car is running it is idling rough and the tac bounces around.

Did you do the test light test?
This is why the U.S ARMY is so good…don’t ask more questions, just do…go…go…go…
What does black wire and IT mean.
lovingly
GTJOEY

Don,
Have you made any modifications to the tachometer, or is it still stock?
Jim

JIM, BEFORE HE FALLS OFF THE TRACKS, I KNOW WHERE YOUR GOING BUT…
OOPS sorry for the caps.
Yes maybe some one put a surpressor or resistor in the line, but basics first.

Perhaps you didn’t get my reply shortly after you suggested the test light. I don’t have a test light I have a voltmeter. The black wire which was connected to the + terminal of the coil was hot. The yellow wire with the black stripe was inactive. So the wiring was correct as you suggested but of course I still have the problem.I have gone through most of the troubleshooting tips from Pertronix and most things appear to be ok except for the coil resistance test. I measured about 10V across the coil . They say you should get about 12 volts if there is no resistance wire and 6-9 volts if there is a resistance wire. I measured about 10 volts.

I also checked primary ignition resistance across the coil with all wires removed and that was about 1 ohm. According to Pertronix , the resistance of the Flamethrower Coil is 1.5 ohms so I don’t know why I read only 1 amp. Maybe it’s an issue with my voltmeter leads.

So dividing the voltage , 10v, by the resistance , 1.0 ohm, gives a total amperage of about 10 amps. If the voltmeter reading was 1.5 ohms as it should have been then the total

amperage would have only been 6.7 Pertronix says for a 6 cylinder car it shouldn’t exceed 4 amps .

Sorry for the long winded explanation, not sure where I go from here??

Thanks for you interest … much appreciated!!

Don

Didn’t get the other one, so it looks as though you have the hot…
The stripe could have been the ballast jumper wire.
Two things left.
Is the coil they sent, does it have a built in ballast?
Try any cheap coil and see if it goes away, as long as 12volt.
Last is the wire to the tach, but 68 was a transition year, tooo many changes.
Just try a standar 8 dollar coil, NON BALLAST.
Good luck.

Tried an old coil that was on the car when I bought it in 2003 and had the same result …ran rough , jumpy tach.

Submitted a ticket on Pertronix site this morning but haven’t heard from them. Will call them tomorrow if necessary .

Thanks for all your help GT-J!! If you think of anything else please let me know.

Don

Your welcome…I don’t think there has ever been a car manufactured with a black hot lead unless the wrapping fell off
It’s time to trace the wire back to the key
People used to put surpessors in the line with a hot coil to regulate the tach
But when you hit a home run to the battery the car runs fine
It’s the black wire source
Follow the light my friend…follow the light!:grinning:

I had a similar problem with the Pertronix on my 68 which does not have a ballast resistor and has tach driven by camshaft generator, not from distributor. So tach was never an issue but plugs would foul quickly. By tracing and testing the wires from battery to ignition switch, ignition switch to fuse panel and fuse panel to coil I found that the ignition switch to fuse panel wire was suspect. There was an old repair covered by insulation tape which when removed revealed a number of broken wire strands. Looked like it had once been trapped by the fold-down instrument panel. I replaced this wire and this resolved my problem.
To summarise, there are only a few wires to trace and test. Easiest way is to have a length of wire and run it directly between each junction point to see when the idle smooths out.
If your tach is driven from the distributor that may be a separate issue.