i have found in the past that a bad regulator or a poor ground on the regulator to body can cause that....check all grounds that seems to be something thats always under rated .... body to motor a quick jumper to the motor to body will tell you
Sparky

LETS TAKE THIS #$^&&*#@ OUT AND SEE IF WE CAN GET IT TO DRIP PARTS
Sparky
72 CUDA 440 10.10 1/4
72 Challenger 340 Rallye..sunroof car