I have a 69 camaro with a 350, my GEN light comes on at idle, but at about 2,000 RPM's it goes off. I have taken the alternator off and it tested fine. I have also replace the plug the plugs into the alternator making sure it was not bad. Can anyone help me with this? Thanks.

 

How long have you had the car? Has it always done this, or just started? Have you tested the alternator with a meter while it's on the car? Do you still have the original external voltage regulator (mounted on the drivers side of the radiator core support)? If so, try smacking it with the handle of a screwdriver and see if anything changes. Or, has your charging system been upgraded to an internal regulated alternator? Do you have a larger diameter pulley on the alternator, or smaller crank pulley? Either one of those would slow the alternator down, and could make it touchy/borderline at idle.

 

Probably nothing orginal on the car.

The alternator may have a larger pulley on it. The belt almost hits the alternator bracket. I guess I could put a smaller pulley on it. Would a smaller pulley do any harm?

There is a external voltage regulator on the car. It looks pretty old and not replaced when they put in a radaitor and engine. I know didn't come with a 350, I think a 327 but not for sure.

I have had the car for a couple of years and sometimes at idle the GEN light would kinda start to come on, but now you have to keep it up around 2,000 RPMs to keep it from not comming on. I have wacked the regulator a couple of times, but didn't seem to help.

 

Measure your alternator pulley and see if it isn't close to 5" diameter. I used to have one on my car, as the v-belt would want to have a tendency to zing off once the engine hit 6 grand. At idle, my charging was barely at a break even point, and less than that at night with the lights on. I've since changed mine over to serpentine. And no, a smaller alternator pulley isn't going to hurt anything

 

2 3/4 inches on the alternator and 6 3/4 inches on the engine. What do you think? Do they make a alternator that will put out more juice at lower RPMs?