Help to diagnose exterior light failure indicator on 87 W126.
 

This is on an 87 300SDL, but I don't think this is unique to any specific engine.

Need help to diagnose why my "Exterior light failure indicator lamp (yellow)" on the instrument cluster is on.
The owners manual states "If an exterior light fails, the indicator will come on only when that light is switched on." "If a brake or turn signal light fails, the light failure indicator will come on when applying the brake or actuating the turn signal and stay on until the engine is turned off".

The dash failure indicator lamp only lights when I press the brake pedal (I can turn on all other exterior lights, all interior lights, and all electrical accessories, and it only comes on when the brake pedal is pressed. I have replaced all fuses. I have replaced both stop lamps with the proper German bulbs, and the problem still exists.

The only other significant item I can think to mention, is I installed one headlight bulb that was 80/100 watt for a few months before I read the warnings on this board, and replaced it with a standard bulb.

Any suggestions to why the brake light circuit triggers the dash external lamp failure indicator?

Thanks, any help would be appreciated.