Slightly off topic (sorry Jerry) but involving car electrics... The other day I pulled into a parking space at the supermarket next to a car with a young mum and her kid.
As I got out she tried to start her car and it did that slow laboured turnover which tells you you're not going anywhere.
So I offered a jump start, she accepted and we hooked up the jumper cables.
However it made no difference! Checked the cables were on properly, gave the clamps a twist to ensure connection, still nothing.
We're scratching our heads when a young bloke and his girlfriend walked over and offered to help. The girlfriend told us he's a mechanic.
He disconnected the negative cable on her battery and clamped it to the engine itself (starter motor housing I think). Tried again, it started straight away.
So there you go - apparently you get a better earth from the engine than from the battery terminal!