If your switches are the same as my '88 740, i.e. separate switches in a cartridge to make a master switch.

Did you keep the old switches?

I recommend an autopsy - if they are burned inside, have your charging system checked - perhaps high voltage from the alternator.

They are pretty easy to rebuild - its in the FAQ. The contacts should have a gently rounded top, like the shape of the top of a frisbee.

The only thing that I did differently from the FAQ, is that after I sanded and burnished the contacts, I turned the rocker around as the UP contacts were a lot more worn than the DOWN contacts.

Did your guy install NEW switches?

BTW - the master switches have a key on on one corner, different corners for each switch. If you cut the key off, the switch can be put in any position.

When I repaired my nephew's switches, I could nit get the driver's switch to work, Itook the switch from the left rear door and swapped it with the driver's switch - he could still lower the rear window with the master switch.