last year my son gave me a portable electric heater for my truck. I think he said it came out of a road tractor or maybe a farm tractor, I don t know.
anyway, it came with about 10 feet of factory wiring with a fuse and ring terminals on the end.
I hooked it up straight to my battery, and used it here and there thru the winter. in early spring my voltage reg. went bad.
I suppose this is related, but maybe not. any ideas on how to prevent it if it was the cause?