[W126 Coupe] More help?

[Dick Spellman]

If you suspect a corroded seat switch as everyone is chiming in.  A short
cut would be to simply remove power from the seat switch unscrew the switch
from the door (2) screws and dip it in a container of contact cleaner for a
minute leaving the soldered harness intact (pre 85) or unplug the harness
(85 or newer). See if that works to restore corroded contacts and save
yourself the aggravation of pulling the unit apart which requires a well lit
tray because of all the small parts (balls, seesaw contacts and springs).  I
did this on the 83 and then just laid the switch and harness in a rag so as
to not mess up the car allowing it to drip dry.

Dick