w123 300d battery light stays on
 

Need your help guys.

Yesterday, I turned the key to turn the car off. The battery light stayed on. Strange. Even with the key totally off, the battery light stays on.

I try to start the car, the glow plug light did not come on but it started fine. This was probably due to the engine still being hot.

I was able to drive the car home without incident but the light again stayed on even after the key was out. I had to disconnect the battery to turn the battery off.

Observations-
The battery light is on and the fuel guage is also working with the key off.
With the key in the 'on' position, the glow plug light is not on.

Last observation, when this happened, I smelled something burning under the hood. Although I did not see smoke, I smelled maybe burning wires?

All the fluids looked fine and there was no obvious burnt wires.

Any ideas?

Disconnect the alternator.

See if the battery light goes off.

This usually indicates a problem with the alternator - bad diode or ???

This article is not about Benzes, but if you read down far enough, it explains why the light stays on when the alternator stops working:

Bosch Charging systems

so if it is the alternator, could i simply replace the regulator?

possibly, but it could be a myriad of problems. the Regulator just maintains voltage, the diode pack converts the a/c voltage to DC that the battery system needs. likely you need the alternator itself pulled and rebuilt or replaced.

had this problem in my 81 240d, just replace the alternator. I bought a new one for $110 and its been great.

Call your local shops and see who can get one the cheapeast. Dont bother just replacing the regulator, chances are its the alternator itself. The new one will come with a regulator.

definitely alternator. my 300sdl also did exact same thing according to maintenance records i was looking thru yesterday. but yes as others already said regulator usually comes with alternators and are replaced as one unit. In the military tho you can usually just order a regulator seperately from the massive alternators on humvees, track vehicles etc. but they are pretty heavy duty alternators that rarely go out