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TR2/3/3A A mystery for Pertronix fans

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TRclassic3

TRclassic3

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a little background first. ive been running Pertronix ignition in my 3A for at least 15 years i have always carefully observed the "don't leave the ignition on without the engine running for more that a few minutes". So I had been working on a light issue and inadvertantly left the ignition on...OVERNIGHT....battery dead the next morning. Fully expecting the Pertronix to be fried I was certain I would need to order another one. After charging the battery I thought I would try to start the car fully expecting nada. Now the fun part...fired right up. Runs and idles fine. Have not taken it out for test spin. Being I would rather be safe than sorry Ill replace the module anyway. Thoughts on why it didn't fry? My other concern is the coil. Reistance measures OK on both primary and secondary coil but again wonder if it can be trusted under load and at higher RPM. Pertronix site mentions leaving ignition on can also damage coil.
 
I’ve also had a Pertronix in my TR6 for over 15 years without a problem.
I’m guessing that if your car starts and runs it will also run under load. As to why it didn’t burn up with the ignition on, I can’t answer that.
Anytime I need to work on my car with the ignition “ON” I always pull the positive wire off of the coil so I don’t burn it out.
 
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That makes perfect sense. Thanks. Wondering if the odds of engine stopping at a point without ground could be as high as 50/50? Likely no harm done in this case?
 
Is it possible that your Pertronix isn't a "I" but a Pertronix "II" or (less likely) a Pertronix "III"? Both the 2 and the 3 have protection from key on, engine not running damage.
From the Pertronix website:

Screenshot_20250515_104255_Chrome_copy_800x150.jpg
 
If the 'pick up' module is black, it's the Pertronix l
The ll is red
The lll is larger and well marked as such
 
One (of many) problems with the Pertronix design is that the distributor's mounting plate is not very good at conducting heat out of the Pertronix module, so it can overheat easily. While it isn't a "given" that you will fry it if you leave the power on, it is a real risk. Maybe it was cool in the garage that time, or you simply got lucky.

If the thing is now working, there is no need to replace it.
 
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