Electrical pulse

There are plenty of grounds between steel and aluminum. I'm 61 and I've been doing this for about 45 years. I'm a retired fully certified ASE school bus mechanic so like I said, all of the normal things have been checked. That's why I'm hoping someone has seen this exact issue and can enlighten me on how to solve it. I spend a few hours here and there on the car (it's a project) and on the internet doing research but I haven't ran across this particular issue with any info on the internet.