On my 1994 Mercedes w124 E320 wagon, the instrument cluster panel with the Indicator Lamp symbols that shows warning lights, the symbol Exterior Lamp Failure came on after I pressed the brake pedal. When I first start the engine, none of the warning lights came after starting the engine. Once I first pressed the brake pedal, the exterior lamp failure light came on and stays on, even when I let go of the brake pedal. When I checked the rear brakes lights using a brick to hold down the brake pedal, all brakes lights are working properly. I suspected the brake light switch located behind the brake pedal is faulty. I was under the impression that if the brake light switch is faulty, the rear brake lights will not come on when pressing the brake pedal. Is that true? I checked all the fuses and all of the fuses are ok. Could there be a short electrical wire somewhere? Do I remove the brake light switch and check for resistance using a volt meter? I am somewhat baffled by this issue and does anyone have this problem? Any ideas/comments or helpful hints is greatly appreciated.

Try 2 rear bulbs or third brake light bulb inspect all contacts at bulb , just sounds like poor contact of bulbs either rear or third brake light

Thanks for the tip above. I will check into that and others as well. Will keep posted on this issue.

dmorgan, remove and inspect the base of the brake light bulbs. With age the contact points on the base develop flat spots, as if they were filed. Replacement lamps should resolve the problem with the warning light on the dash.

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Fred Hoelzle

I inspected both bulb sockets on the back rear lights. While inspecting, I noticed the so called third brake stop light in the lower center of the windshield without the covers. The electric windshield wiper motor is attach to a bulb socket that I assume is the so called 3rd brake stop light. The bulb socket is empty. When I put in the bulb in the socket, nothing lights up. Also, when checking the bulb sockets contacts on both the rear brake lights to make sure the bulbs makes contacts by running the engine in reverse and parked with all headlights on along with the brake pedal being squeezed using the brick as leverage, all 4 lights on each bulb sockets came on, except the middle 3 brake light. I am going to test the 3rd stop brake light for resistance. Will follow up on my progress. Thanks to all who wrote and read this particular thread/issue.

I just finished checking out the third stop brake light and used electronic cleaner (CRC) on the both contact point with the 12 volt watt 21 bulb. It seems to me that the light socket was not secured enough probably due to age and bouncing around, etc. Now when I see the third brake stop light works and restart the engine, the Exterior lamp failure warning light went away. While I was doing some research on the wattage on the exterior lamp bulbs, here is some information on the various locations with the wattage showing below:

E-CLASS 1993-1995
W124
High & low beam headlamp 9003
Parking light P21/5W
Front turn signal P21/5W
Rear turn signal 7507 Amber or PY21W
Tail light 12814
Stop light P21W
High mount stop light P21W
Fog/Driving light H3-55W
License plate 12844
Back up light P21W
Front sidemarker P21/5W
Rear sidemarker 12814
Dome light 6411
Trunk/Cargo area 6411
Instrument-general 12256

Thanks to all who shared their comments/reading this thread.