I've got an 85 300SD where the battery light (and AntiLock Brakes light) stayed on after starting, but once I got the car up to speed the lights went off. When I put the multimeter on it when I got home the voltage at the battery was 12.4 and dropping slowly. Once I reved the engine up the reading went to 13.6 and was rising a bit.

I just replaced the alternator and the pigtail wiring bundle that plugs into the alternator( due to a frayed wire) about a month and a half ago. Not sure if its related but I don't want to leave out anything that might be useful.

Any ideas why this might be happening?

Thanks

 

the exact thing happened to my sons ...i brought the alt bac to rebuilder and he fixed it.

 

Thanks guys. I replaced the alternator and everything is working great.