I’ll bite.
Years ago, as teenagers, my brother and I shared a $600 station wagon with a $99 paint job. It actually ran pretty good. But we tinkered with it constantly adding stereo systems, PA systems, etc. (usually bought at garage sales). The PA system was an AC powered system originally intended for a building, not a car.
Anyway, the car developed some “electrical problems” that could not be diagnosed. And we did spend too much money taking it to a mechanic trying to figure it out. Hit the horn and blinkers turned on but horn didn’t work. Sometimes turning the lights on would also turn the windshield wipers on. To turn them off, you would have to turn the wipers on and turn them off again. If that didn’t do it. Stop and restart the car (no kidding). The PA system and the living room speakers for the stereo worked fine though.
We didn’t tell my dad about all the problems because we figured we had somehow caused them. The first mechanic could find nothing wrong with the cars manufactured wiring (fuses and such) - $50. We took it to another mechanic and he discovered that “the polarity of the cars frame had been reversed and the grounding system in the car was no good.” He explained that he thought systems in the car were actually getting power through a now energized grounding network (through the frame of the car?). He actually showed us where he could read a current by touching a lead from his meter to the chrome bumper. We asked how to fix that. The guy said, “I have no idea. It would be a hunt and test project billed by the hour.”
We said thanks and paid the guy $100 for telling us the car was never going to work right again. I wasn’t as engineering savvy back then as I am today. But I am still stumped as to how this could happen without blowing fuses and causing significant issues for all systems. How does the battery not just drain out immediately?
BTW - I am NOT an electrical engineer and grounding is still a bit Voodoo to me.
That is a bit of a puzzler.
Sounds like my Fiat!...............
That's because it actually didn't happen. The $100 you spent was to someone who didn't know what he was talking about.
Most cars especially of the vintage you described, can develop problems where the ground wires connect to the frame and body. This happens especially quickly where road salt is commonly used. This means that ground (-12v at the battery) really isn't -12v, it's somewhere higher than that, depending on how good the connection is where you're measuring it, and how good the connection is at the battery. This can vary depending whatever the electrical draw is and whatever the generator (alternator) is providing. The only effective long term fix is to remove and wire brush every ground connection on the vehicle. You really only need to do it to the bad ones, but you really can't tell which is good and which is bad.