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Questions and Answers

Mercedes Benz 300D Lighting

Q. Hi Vince, You are my best hope for some guidance here: 1983 Mercedes Benz 300D 171,000 miles. I'm having external lighting problems and don't know where to begin trouble shooting. Directionals and 4-way flashers work fine as long as the headlights are off. With headlights on, 4-way seems to work okay and the left-turn directional seems okay.

Mercedes Benz 300D Lighting

Right turn directional flashes as long as the brakes aren't applied, press on brake pedal while right directional is flashing and it stops flashing. Does not happen with left. I changed all rear bulbs, both sides, with correct wattage/type Mercedes Benz bulbs.

Cruise, which uses the light bulbs for control is working okay. Headlights/fog lights work okay, high beam is fine too. I need to start replacing parts but am unsure where to begin.

Does the car have a separate flasher for the directionals and 4-way or is it all in the same unit? Grounds for the rear lights look fine and tight.

Thanks Much Vince, greatly appreciated.

A. These old Mercedes Benz cars are an electrical nightmare. I have the same car and I have a tachometer that works once in a while, cruise control that will start working halfway between Minnesota and New Jersey, as long as I don't shut off the car, and a left rear power window that doesn't work when the temperature goes below 40°.

It has one flasher for both the turn signals and 4-ways. It should be underneath the dashboard by the steering column. What I do is turn the signals on and follow the sound of the flasher.

Before I start replacing parts, I would examine the harnesses very carefully. This car had a tendency to have a wiring harness rub through and cause all kinds of problems. I would also check the terminals inside the connectors and make sure they are clean and tight. I have seen many times even though a connector is plugged and locked, because the terminals are so loose they still don't make contact.

And maybe someday I'll get caught up here and have time to work on my car.

Additional Information provided courtesy of ALLDATA

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