R129 Bulb out Warning

[Biglee]

Any suggestions from knowledgeable members appreciated. Fixed all minor electrical gremlins in my 1990 500 SL apart from one which is bugging me marginally.

Any one have info on the bulb warning system. When I use main beam or flashers the warning lamp in the dash comes on to say I have a failed bulb. When I haven't.... I have read different voltages can cause it but bulbs are identical new bulbs, both lights are exact same brightness. It is only a minor irritation but would like to get to the bottom of it. Anyone know if there is a ECU to control this feature and where it would be on a 1990 SL.

Many Thanks Lee

 

[whitenemesis]

Chassis earth connections?

 

[RichardF]

Just a random thought. When you put main beam on are all the bulbs working ok.
Side, both tail, number plate?

The main lighting ECU controls all this stuff. It's under the fuse box and labelled "Hella"

 

[Trickythemerc]

I had a very similar problem with my Jaguar,it would throw a bulb failure warning for the O/S brake light every now and then. Took the bulb out,looked ok put it back and all was well for days or weeks. I tried using a remote earth,still the same until one day I dropped the bulb and it broke the glass. Fitted new bulb problem gone for good.

From this I learnt that there are some pretty nasty cheap chinese bulbs about and this could have been the cause. The bulb may look OK and work fine but could have a lower resistance value than a quality bulb and this will trip the failure warning.

 

[BTB 500]

I would check the bulb and holder contacts to make sure they are clean and shiny.

We're getting an occasional warning for the right hand reversing light on our C Class, so that's on my list of things to do. The light works correctly and the bulb is the same one that was in the car when we got it 2+ years ago. The warning only started last week.

 

[Biglee]

All bulbs work OK. The bulbs are brand new and identical Halfords super brilliance or something bulbs. Bulbs holders all clean and shiny.. was same before I changed the headlight bulbs so I dont think it is teh bulb or holder - In fact I have since changed one of the headlights and still the same. I will look for the lighting ECU later tonight and check connections. Thanks for tips so far - keep em coming.