Pesky Ext. Light Failure Indicator Lamp
 

OK, I wanna get that damned light to go off on my 86 300E dash. I have NO Exterior lights burned out, but the light unrepentently burns. Is there an easy way to disarm this function other than removing the instrument cluster and pulling the bulb? BTW I vaugely remember that the wire that powers the sensing unit is at the same wire block (on the LH fender, under hood) where the field exitation wire for the alternator is located. Can I just discoinnect this wire or will is cause some stupid and completely unrelated catastrophic failure of some other system I am not aware of......thanks Clip

Double-check:

- Center brake light lamp(s)
- Licence plate illumination lamp(s)
- left and right lamp pairs are the same wattage and manufacturer

These have been known to be the 'sneaky' causes of stubborn failure lamp.

Imbalance, due to complete failure or differing size or sometimes brand, can be enough to trigger a false alarm.

Hint: center brake light fault does not occur until brake pedal is pressed.

I had the same problem until I discovered that the side marker light in the rear was out. It is not readily obvious that it is blown.

don't take it on the warning light, it is just doing its job.

Rather than disconnecting a bunch of wires and perhaps causing woes, why not place a strip of electrical tape over that warning lamp? Not practical, but it did do the trick on moms Oldsmobile when the "ETS" (traction control) lamp was staying illuminated.

If I understand your post, the light is on even when no exterior lights are being used. The light should only come on when you select a function where the bulb is burnt out. For example if a directional light is out, the dash light will come on only when you use that signal. I have the exact same problem in my wife's 89 300CE. It comes on as soon as the car is started and stays on til the car is shut off. It's been on a few months now, because I haven't had time to fool with it. I will trade cars with her tomorrow and check it out. I suspect a module, but I'll let you know. By the way she's had all kinds of MBs, but she loves that little coupe even over the SELs. We drove it to Vegas a couple of weeks ago. I let it stretch it's legs at 80 to 100 MPH during some long straight stretches through the Mahave Desert and Dealth Valley with no bears around. That M103 really performs.:D

It's not the sensor, you have a lamp out, find it and replace it, use the process of elimination, start with the parking lights, reverse lights, headlights, high beams, fog lights, brake lights and lastly turn signals, turn signal trigger keeps the light on until you reset the ignition key

It happened to me...
 

with a 1988 190E. All the exterior lights worked fine but the dash indicator never went off until I discovered a replacement bulb was not the same type as the others. The replacement bulb had a gold base rather than a matching silver base and that difference was enough to trigger the warning light on the dash.

The light failure lamp will illuminate if, for example, your two brake light bulbs are different from each other. Or right/left tail light bulbs.

This system depends on OEM bulbs (German) and correct bulbs in every socket.