I had an 88 420SEL that had the same issue.
I'd just about forgotten about it by the time I got around to pulling all the fuses, cleaning the contacts with a Dremel and wire brush and replacing the plastic bodies fuses with ceramic ones with copper filaments.
Once I was done with the job, I just happened to remember to try the switch... Damned if it didn't work.
I'd just about forgotten about it by the time I got around to pulling all the fuses, cleaning the contacts with a Dremel and wire brush and replacing the plastic bodies fuses with ceramic ones with copper filaments.
Once I was done with the job, I just happened to remember to try the switch... Damned if it didn't work.