Wacko Wiper W124 - Relay?
 

My 1994 W124 E320 Wagon has an intermittent wiper problem. The wiper comes on sporadically in intermittent mode when you indicate a left turn (never happens with a right turn signal). It also sometimes comes on for no reason at all - always in intermittent mode. I searched this site and decided that it was the combination relay. I first took out the relay and cleaned the contacts - it was the original relay I believe and the contacts were moderately corroded. Cleaning the contacts made no difference at all, so I ordered the replacement from Mercedesshop. I just installed the new one and the problem is NOT THE SAME BUT STILL THERE - now when I signal for a left turn it takes 5 or six seconds / clicks before the wiper goes intermittent and sometimes it does not ever happen. I wonder if there is any way to clean the sockets the contacts go into? Or is there likely some other problem like the wiper switch? Anyone with similar experience please help - wife is not happy I just spent $80 for the relay and the problem is still there. Come to think of it, I'm not that happy either!

I think the way to solve this mystery is to figure out what the combo relay and the turn signal have in common.

I'm not looking at a wiring diagram, but I kinda doubt there's any commonality in the electrical portions of the wiper and signals. Sometimes really odd behaviors happen when a ground point goes bad (corrosion blocks it from conducting electricity) and the current seeks another path to ground. It's worth checking the manual to see if the wiper relay and the signal flasher share a ground point, but I'm betting the answer is no.

Both of these functions are activated by the same stalk. I wonder if there's a broken wire or damage to the wiring insulation inside the stalk or somewhere in the steering column? That's where I'd look first.

- JimY