Bizzare Electric Problem - PeachParts Mercedes-Benz Forum

bgoodeve · #1 12-16-2003, 07:17 AM

I could use a little guidance in tracing an electrical problem in my 93 300D 2.5 Turbo. Symptoms are as follows:

With key to "on", left bank of indicator lights are out. and right bank are dim. When this happens, upon starting, the charging circuit does not charge the battery. Also when this condition is present, pad wear indicator light and SRS light will be on, and directionals will flash but there will be no relay clicking (there is nothing wrong with pads or airbag). If driven too long like this battery will eventually die. However, sometimes, after shutting down, all will be fine, as though something has reset. With so many relays, etc. kind of have no idea where to start. Replaced the multi-function relay just cause I had one around. That didn't fix anything.

Thanks, Bart

leathermang · #2 12-16-2003, 07:57 AM

Have you considered buying the electrical vol of the Factory SHop Manual ? Might be worth it rather than throwing more money at parts......

bgoodeve · #3 12-16-2003, 01:26 PM

Have the shop manual, and happened to have the relay mentioned lying around. Was simply wondering if anyone had run into this and could narrow the search.

Rick Miley · #4 12-16-2003, 01:30 PM

This is not advice to blindly change parts, but rather a place to start investigating. All sorts of wacky electrical behavior on W124s has been traced to a faulty Overvoltage Protection Relay. Perform a search here for details.

bgoodeve · #5 12-16-2003, 03:49 PM

Thanks, Rick. Will start diving into this later tonight.

bgoodeve · #6 12-22-2003, 03:58 AM

Well, all the odd and intermittent indicator light behavior aside, the problem turned out to be sticky brushes. Tested out the overvoltage relay (I was so sure it would be the culprit) and it was just fine. Decided to come at the problem from the other direction (charging circuit), replaced weirdly worn brushes and voltage regulator and all is now good. But I must say, I'm more used to a failed charging circuit triggering a warning light than putting it out.