W123 had issues I thought were switch related and were not

Check grounding points at both front corners and at trunk (boot)

get a wiring diagram and check all wiring and do not assume connectors are properly
assembled if it's a used car.

If it was working for you at some point it might just be a grounding issue.

Get a DMM digital multi-meter roll your sleeves up.

if you take anything apart use di-electic grease upon reassembly