Odd Heater/AC Blower Behavior 300SDL
 

1987 300SDL
Sometimes the heater/ac blower will not come on until I pull the turn signal stalk back to flash my bright lights without the headlight switch being on. I do not understand electronics very well, but I’d like to trace this down. Any pointers?

Two things come to mind:

1) Blower motor brushes are worn. Does it come on immediately if you set it to defrost?

2) Key switch is worn. Does jiggling the key get the blower blowing?

There’s a dozen other things it could be :/

Sixto
98 E320s sedan and wagon
02 C320 wagon

Since those two circuits have nothing in common with each other, I'd suspect our old friend, the bad ground. There's a group of grounds behind the instrument cluster and another behind the center console. Wonky ground connections can cause all sorts of bizarre behavior when one circuit starts back-feeding through another when it isn't supposed to.

Thanks!
 

I appreciate the replies. I think I’ll start with the grounds behind the console. There have been a few times that I could get it to kick on by bumping the console on each side near the climate control unit. Now when I want the blower on I just select the setting on the unit and then flash my headlights and the blower comes on...every single time.