Actually *every* exterior light bulb passes independently through the bulb out detector relay. Only exception is the turn signal lamps, they come off the turn signal switch, there is a line to the detector relay from the turn flasher, that looks for the 'fast flash' as an indication you have a bad turn signal. But every other filament has a dedicated line back to that relay.

This is the extra large relay in the control box behind the fuses. They are known to develop internal bad connections as the current for each lamp has to go in and out of the relay and through a sensing shunt inside.

Had a intermittent marker light failure on my 124 that was caused by this relay. Drove me nuts until I figured it out.

Do you have the schematics for a 124?

__________________
The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech