I installed a internal coil HEI in my 292 GMC about 20 years ago. The GMC uses a cloth covered ballast resistor wire, which connects from the firewall plug/connector to the distributor coil. I had disconnected the ballast wire and ran a copper wire with HEI connector in its place. After installing the HEI and setting the timing the HEI module burned out on the third time I started the engine.
I believe it was because of the mechanical voltage regulator as efi-diy pointed out. I removed the new wire and put the HEI connector on the ballast resistor and have not had reason to change it in 20 years. The 1.8 ohm ballast only drops about 2 volts. With 13.5 V from the original ex reg alternator at idle, I still have 11.5 V at the HEI. That equates to just slightly over one Amp and has not caused a problem with the ignition switch in all these years. The slightly lower voltage and the added resistance reduces the chance of damage from a voltage spike.
I did replace the internal coil HEI with an external coil HEI about three years ago to get more clearance for the Sanden AC compressor.
The AC unit is an electronic Climate Control from a Lincoln with two small diameter pusher fans from Cadillacs. One has 208 degree switch and has never turned on.
Still have the same 10DN external reg alternator.
The original HEI module was an aftermarket piece and not considered as reliable as the GM module that I have now. The regulator is now a replacement with semiconductors inside instead of relays.
It all works for me and I don't carry a spare anything.
