[legion]

What type of vehicle and how old?

On my 951, something wouldn't work right unless it was at exactly 13.5 volts. (Mostly the gauges would read low.)

On that car, I ended up rewiring the headlight, replacing the main ground, having the alternator rebuilt, cleaning all of the other grounds, and replacing the battery before the electrical issues were completely solved.

I took the car to an Interstate Batteries shop at one point. They had the voltage at 13 even when the car was running, and said everything was fine. It wasn't.