This is for the 1991 560SEL. The exterior lamp warning indicator lights when the light switch is turned to the right (parking or full head lamps on). The #6 fuse appears good, so I replaced both the third brake light and both brake lamps, still no joy. Noticed one of the license plate lights is out, could this be the problem? Or, possibly the brake light switch?

Does the warning light only come on only after turning the park lights or headlamps on? Have a helper run the various light positions while you go around and check all the lights. IIRC the licence plate lights are connected to the warning system.

__________________
1989 300CE

Could be the license plate light. Could also be the bulbs--the resistance of Osram bulbs is about the only thing that makes that system happy. Most everything else will make it think there's a bulb out.

__________________
Earl McLain
'02 C230 Kompressor
'89 560 SEL "Frau BlueCar" (retired April 2004)

Thanks for the replies, I'm going to try the aforementioned solutions and post back with results.......

On my 97 E420 if even just one of the two license plate lamps is out, I get the message on the instrument cluster. It took me forever to find the bad bulb the first time this happened. The S430 gives me a much more specific message to id the bad bulb.

__________________
1996 C280 289K Traded
1997 E420 167K Traded
2001 S430 240K Traded
2010 E550 4matic 80K
2000 GMC Jimmy 198K Gone to Boneyard
2003 Camry LE 196K
2011 Mazda3 i Sport 31K

Plate lamp will throw it, just one will do as mentioned.

If it was a brake light, the warning light comes on when you apply the brakes. Then off when foot off. At least that is how it worked in my car.

__________________
1991 560 SEL / 185k miles
1992 750il / 17k miles - project car

Replaced all the bulbs with Osrams, finally the exterior lamp out warning indicator turned OFF. However, when I press on the brake pedal there are still no brake lights. So....I took an emery board to #6 fuse and removed the lamp control module relay and cleaned the contacts with an emery board then sprayed everything with electronics cleaner. I then allowed it all to dry then reassembled. Still no brake lights! I'm thinking I need to check the brake light switch under the brake pedal........what is the best way to check it out?

Un-plug the wire connector, key on check for voltage, do not re-connect the wire until after the switch is tested.

Ohm test the switch brake pedal applied and off, no change = bad switch.


.

__________________
ASE Master Mechanic
https://whunter.carrd.co/

Prototype R&D/testing:
Thermal & Aerodynamic System Engineering (TASE) Senior vehicle instrumentation technician.
Noise Vibration and Harshness (NVH).
Dynamometer.
Heat exchanger durability.
HV-A/C Climate Control.
Vehicle build.
Fleet Durability
Technical Quality Auditor.
Automotive Technical Writer

1985 300SD
1983 300D
2003 Volvo V70

https://www.boldegoist.com/