View Full Version : Ballast resistor location....

07-10-2009, 11:37 PM
Hi All!
I'm glad to be here!...Recently purchased 74 TR-6
Awesome shape.Have done a lot to it in the last month...Pictures coming as soon as I figure out how to upload...lol
hey i think i figured it out!
OK down to business...I did a GM alternator conversion as my original was faltering and it seemed silly to put back a 28 amp unit when the Delco conversion was less then a hundred bucks. I also did it so the Pertronix Ignitor electronic ignition and coil would get at least 12v(which apparently is imperative)..
The Ignitor went in ok but ran like crap...put the points back in....Hunted on the net and found out the plugs had to be regapped to 45 thou....did it , ran great.When you re set the timing it's right off the scale...The problem with the misfiring is back when you accelerate quickly. I tested the voltage from the alternator ...Strong 14.7v...From the new coil positive and ground, it's 11.4v...there supposedly is a ballast resistor in the 74 but I'll be %%^%##@#ed if I can find it. I have to remove it, to get the volts up on the coil, and the coil has a resistor in it...HELP..Oh, Pertronix were zero help with the Ignitor problems, never even responded to my Emails...
Look forward to your input!...stan

07-11-2009, 12:35 AM
The ballast resistor wire is buried in the wiring harness. If you strip back the outer covering, it will be the pink wire with the white tracer. But you might as well not look for it and just run a new wire to the coil, since you'll have to do that anyway.

ISTR that the fuse block is not too far from the coil on a TR6, so you can just tap into the white wire at the fuse block and run a new wire over to the coil. There might even be an extra terminal available on fuse block.

07-11-2009, 12:39 AM
I'm not sure if this is the case with mid-70s TR6s or not, but look at the color of the wire(s) supplying coil (+) from the ignition switch. If the original wiring supported a ballast ignition, there should be a white/yellow wire going from the starter solenoid to coil (+). There should either be an external ballast resistor (typically piggybacked on the coil) OR there may be a "pink" wire on coil (+) coming directly from the ignition switch. If you do not find an external ballast resistor BUT you find the pink wire... the pink wire IS your ballast resistor. A non-ballast (standard) ignition system will not have the white/yellow wire and coil(+) will be supplied by a white wire.

The deal with Pertronix (as you've found) is that the electronic module needs to receive a full +12V on its "red" wire. You can still use Pertronix on a ballast ignition system as long as the combined ballast resistor and coil resistance is not too low. (Anecdotal evidence indicates that the total needs to be greater than about 2.3 Ohms). For a ballast ignition system installation, the black Pertronix wire still goes to coil (-), however, the red wire must go to a switched +12V source... NOT coil (+).

If you want to figure out what's going on with your ignition and you're simply not sure what's there, connect one multimeter lead to coil(+) and connect the other lead to a ground point. Put a jumper wire on coil(-) and connect it to ground. Turn the ignition switch to the run position and read your meter. If you find 6V to 9V, you have a ballast resistor somewhere. If you measure 12V, then you do not have a ballast resistor or resistor wire.

The increased gap on the spark plugs isn't mandated by changing to Pertronix but it is a step often taken to get higher spark voltages, often with increased performance.

From your Pertronix research you may have also found the following. To protect your module, do NOT leave the ignition on with the engine NOT running for more than about 3 minutes at a time. The module is not meant to be conducting 100% of the time and that can happen with the key on and the engine off.

07-11-2009, 12:47 AM
The increased gap on the spark plugs isn't mandated by changing to Pertronix but it is a step often taken to get higher spark voltages, And increased rotor failures.

07-11-2009, 08:48 AM
I've been running a Pertronix in my 74 for better than 2 years.
I noticed you mentioned a "new coil" in your post. Is that coil for a ballasted system or for the 12 volt system that you may be trying to convert to ?

I think that some misconception comes from the fact that the "generic" installation instructions show how to wire the "switch" for a ballasted system that commonly reduces the coil feed down to 6 volts. The TR ballast wire provides more, much more than 6 volts. Pertronix says (on the box) it can work in the 7 to 14 volt range. If you still have the box, check it out.
If you do decide to bypass the resistor for coil voltage (not necessarily the Pertronix switch) just be sure that your coil is a 3 ohm coil designed for the constant 12 volt feed.

As far as plug gap,.045 is quite a bit for reliability. I don't think you'll ever have a misfire with the gap at .032 to .035.
You won't have a problem getting combustion in a TR6 with that gap. Check your plugs for color after a couple hundred miles.

07-11-2009, 09:27 AM
And increased rotor failures.

I suppose that would indeed be a side effect of the higher voltages. I personally haven't increased the plug gaps on my cars with electronic ignition so I have no first-hand experience with the "downside" of opening the gap.

07-11-2009, 07:14 PM
RynoBoy........good advice up above so the only thing I'll add is my broken record electrical pearl of wisdom: First - download the free color wire schematic for your car from AAW. Dan Masters created these due to the mistakes and inconsistencies in the factory schematics. (https://www.advanceautowire.com/tr2506.pdf) The other thing you should buy is Dan's TR6 Electrical Maintenance Handbook available from Moss and TRF.

07-11-2009, 08:49 PM
I can't thank you all enough for your invaluable input...In the morning I'll re gap to 35 thousand from 45....See if that makes a difference...Yes I'm running the 40000v 3.0 ohms coil from Pertronix..
Dan Master's was the one I referred to for alternator conversion...Awesome!!!!

07-11-2009, 09:13 PM
With that coil, you should bypass the resistor wire then. If you feed it less that 12 volts,it won't be able to put out it's full potential.
Since you are familar with Dan Masters, here's one of his articles.
Down at paragraph 5 he tells you how to bypass the TR6 resistor wire.

07-11-2009, 09:15 PM
Here's a link to an article Dan Masters wrote for the Vintage Triumph Register that details how to bybass the ballast resistor. Very easy to do on a '74.


07-12-2009, 11:29 AM
David David....Thanks!
I bypassed the original positive coil wire from the relay to the switched fuse, regapped to .0035....AND I got my torquey, angry sounding TR-6 back!!!...NO misfiring....STRONG running, smooth idle.Chirps into gear..I wanna cry...Thanks SOOOOO much for everyone's insightful help!! I luv you guys!!!

Double Cheers!!!