I’m digging deeper on a question I posted earlier. My 1986 190e mb has a weird short or something that causes the wiper to turn on when I turn on the headlights. Any ideas ?
Double check the ground connections of both.
Thanks I’ll check them both but how do you efficiently check the grounds to make sure they are good?
with the load on (wipers running, etc) put a voltmeter between the ground at the load and the chassis (or the negative terminal of the battery). Should read less than 1 volt. Alternately touch a piece of heavy copper wire (#12 or better) between the ground at the load and chassis and see if it changes the situation.
If there is no specific ground wire at the load, then it is grounded via its mounting bracket. try adding (temporarily) a ground connection between the metal of the load item and a good bare spot on the chassis (or the negative terminal of the battery).
Thanks Bill for the info I’ll follow-up. Your the best
Although 1986 was years before the infamous Mercedes “Green bio-degradable wiring harness” fiasco, I’d check the wiring harness under the hood. The 190E’s get plenty of under hood heat, and I’ve seen a couple of examples of broken insulation allowing two wires to come in interment contact (i.e. a short).
Also double check any “customized” equipment for bare wires touching. Prime locations include after market stereos and lighting.
And of course, as stated, check the ground straps under the car. They’re now over twenty years old and live in a hostile environment.
actually I think benzman has a better scenario, a short between the wires to the wiper and headlights. This better explains the symptoms. Easy to verify, put a voltmeter from wiper motor hot to ground and turn on headlights. if you see 12 volts, then there is probably a short as benzman said. But check the grounds also. I wouldn’t try to fix the harness, but instead remove the existing wire and run a new wire from the wiper motor to the wiper switch. You have to look at the wiring schematic to determine exactly where to connect it. Use high quality wire (preferably teflon insulation).
Thanks Bill and Benzman I will check out everything you suggested on my next day off. Your the best…John