'83 300D idiot lights stay on after car is off... - PeachParts Mercedes-Benz Forum

#1 01-22-2003, 04:50 AM

...Specifically, the brake, brake pad wear, and battery light along with the low fuel light stay on after key is removed from ignition. If fuse #12 is removed for a second, they do go out and stay out until car is restarted. What is the problem here? I don't want another dead battery -- Mike

Jim Anderson · #2 01-22-2003, 11:09 AM

Once I had the alternator light come on when I took the key out. It turned out to be a shorted diode in the alternator rectifier.

TX76513 · #3 03-19-2007, 09:35 AM

Jim I have this same problem with a 126 - battery light remains on only after key is removed (or in off position). The brush pack is new and charge rate running is 14.7 Volts, battery is in peak performance.

david s poole · #4 03-19-2007, 09:44 AM

while that light is on the battery is being drained,if you are lucky it's the alternator regulator,otherwise it's the alternator diodes[requiring another alt].

TX76513 · #5 03-19-2007, 10:08 AM

David help me talk my way through this - My car has the internal brush pack with regulator not the external - so if a new brush pack has been installed that would leave the diode which is an internal item?

david s poole · #6 03-19-2007, 10:29 AM

yes that is correct,the terminal on the alternator that has the small wire on it is supposed to be ground until the engine starts and the alt is turning.so if you disconnect the small wire from alt with ignition off and then all your lights go off you can confirm the diagnosis.by the way how old is regulator and why was it replaced?

TX76513 · #7 03-19-2007, 11:23 AM

Quote:

Originally Posted by david s poole

yes that is correct,the terminal on the alternator that has the small wire on it is supposed to be ground until the engine starts and the alt is turning.so if you disconnect the small wire from alt with ignition off and then all your lights go off you can confirm the diagnosis.by the way how old is regulator and why was it replaced?

The new brushes were put in last winter as just some PM while to car was put up. Virtually ten miles on them. They are OEM Bosch. I disconnect that ground and see what happens. Must be going to be an alternator month