I would also measure charging voltage with the engine running. Maybe you are over-charging. At higher than idle RPM, where max output would be high.

"Possible causes are: Faulty charging system (stuck or shorted regulator/alternator)"

Edited October 8Oct 8 by Zed Head

I just re-ran the voltage drop test and its currently showing around 12 volts with the LED not blocked and I think 1.5 volts when the LED is blocked. I tried driving it around for 20 minutes to force it to fail but all I managed to do is annoy my neighbors by making a lot of noise.

Why are there two ballast resistors? I'm assuming that I have a total resistance of 3.0 ohms with the three terminal resistor providing 1.3 ohms and some fraction of that on the middle terminal.

Possibly change the system to a higher resistance coil? And get rid of one or both ballasts. Just a thought

I'm unfortunately working out of town for the past few and next few weeks so I have only weekends to address this issue. Mallory wants me next to my car when the give tech support which makes it difficult. Looking at my notes from last weekend I think there is an issue with a ballast resistor once it warms up.

If you look at my sketch in a previous post as reference, with the engine running after making sure the Uni-lite drops its voltage to 1.4V when the sensor is blocked, the voltage into the top resistor (R1) is 13V and out of the resistor to ground is 9.5V. The output from R1 goes to the bottom resistor (R2). R2 shows 9.5V in and 5.9V out.

After running the car and letting R2 warm up to 120F, the resistance of R2 is 45 ohms. It previously was 1.7 ohms. So if I measured it correctly (the terminals are a bit hard to get a good electrical connection), the resistance of R2 increases as it gets warm which would drop the voltage to the coil. I should of confirmed this but I can do so on Saturday.

Could an increase in R2's resistance cause the voltage to drop to the point where it will not permit the ignition, specifically the Uni-lite, to operate?

I've found most automotive electronics don't like being in the 9v range. And yes, conceivably, high resistance could lower the voltage significantly

I didn't really pay attention to the two ballast resistor part. Did you buy the car with the Mallory already installed? I could imagine somebody adding a resistor if they thought the module was overheating from too much current. But it's obviously not what the instructions call for.

If it was mine I'd probably start from scratch and wire it up exactly like the instructions say, and make sure that all of the connections, including the distributor ground, were clean and solid.

And also measure maximum charging voltage at RPM above idle speed. The external regulators can allow 15 volts when they're working correctly and I assume more if they get out of adjustment. Maybe somebody tried a bunch of stuff to fix/bandaid an overvoltage problem then never removed their attempts after they fixed the real problem.

Edited 4 hours ago4 hr by Zed Head