'94 SL600 washer problem, odd!
 

We have a customer's '94 SL600 at the shop now which is exhibiting a strange problem in that when you turn on the parking or head lights, the headlamp washer pump starts running and won't stop until the key is turned off. If you just activate the right side parking light independently of the other one, the pump still comes on (or at least is energized). Washers work normally when the headlamp washing system isn't activated. Also, the right side headlamp wiper motor doesn't park itself every time. A problem like this seems to me like a bad headlight wiper motor. This car does need an engine harness and LH control units but that should be a totally separate problem. Since we primarily deal with vintage Mercs, I'd love some insight on this problem from you "modern" car guys!

Aaron,
My only suggestion is make sure the wire harness plugs have not been switched on the rear of the headlamps. On many of our cars the plug for the headlamp washers/wipers and the park/turn lamps are both six pin and will interchange. This usually occurs following a front end repair in a body shop.

I can comment . . .
 

. . on the wiper motor: the fact that it doesn't park itself everytime, means it's bad. I've seen this problem before; no park - no good!

Not sure if this is any help...
 

But a few years ago I had a CD from Popular Mechanics with tech info for the R129. I remember seeing a service bulletin about windshield washer pumps not shutting off. M-B's solution was to update the washer pump with a different design and part number. I no longer have the CD.