Why is my generator light always a little bit on?

Dear Car Talk

Dear Car Talk | Jul 01, 1992

Dear Tom and Ray:

The generator light on my 1980 Chevy Citation stays dimly lit most of the time. But I've taken it to a mechanic and the alternator has checked out fine. What's the problem?

TOM: The problem is the guy who checked your alternator, Tom. Alternators aren't like lightbulbs, which either work or don't work. Alternators can "sort of work."

RAY: Kind of like my brother.

TOM: Very funny. Seriously, Tom, the question is not whether your alternator is putting out electricity. It IS. The question is whether it's putting out ENOUGH electricity. And yours isn't.

RAY: And that's why the generator light is on. The fact that it's on dimly means that your alternator is just slightly under-producing. If it wasn't working at all, the light would be shining brightly.

TOM: You need either a new alternator, or a new voltage regulator (which is built into the alternator on this car). If I were you, I'd get a rebuilt alternator, which should cost you around a hundred bucks.

Get the Car Talk Newsletter

Got a question about your car?

Ask Someone Who Owns One