First off, this is my first post here so its nice to meet everyone!

My car is a 2002 ML500. The car had a factory hitch installed at 5000 miles (car is currently at 96,000 miles) and there is something overdrawing the amps on the brake lights when the trailer is connected. This problem developed last year. I know its not a problem with the trailer as I have tested the trailer with two other cars and it works fine.

Basically the directional indicators work, the parking lights work, but the brake lights work only for a second then the fuse in the ML (#15, 10 amp for the brake lights ) blows. Ive tried replacing the Delphi control unit in the rear of the car, but the problem persists. Once, while raining, the trailers electric brakes also engaged intermittantly on my driveway while going very slowly (thank goodness) even though I have no brake controller in my car.

Any ideas what the problem could be? I suppose it could be the wiring from the Delphi control box to the actual 7 pin female attachment point, however I have inspected the connector and no corrosion could be found. I tested the continuity of the pins and there is continuity between some that should not be conducting (cant remember exactly which). I suppose the next step is to replace that female 7 pin adapter, but I'm hoping this may have happened to someone else before.

Thanks for any help!

Jon

Here's some towing info including the electric diagram for connecting a trailer. Hope it helps troubleshooting the problem.

http://www.whnet.com/4x4/towing.html

I once had all boat trailer lights turn on like a Christmas tree when any single circuit lights should have come on. Turned out to be a corroded ground connection....

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W163.154, M112.942, 722.662, ZF.970.402

Don't know if you solved this yet but-

If the trailer has brakes and you don't have a barke controller installed in the truck, the fuse will blow. That's because the wiring harness takes power from the brake light circuit and sends it to the elctric brakes. They draw too much and pop the fuse. When a brake controller is installed that wire is cut.

I'm having the same problems with my '03 ML500, with a brake controller installed. I had no problems with the same trailer and my '99 ML320. After sitting, the brake lights work fine - once. After you let off the brakes, the lights won't come back on nor will the directionals work (actually, the directionals do come on, but so dimly as to be not seen). The electric trailer brakes seem to work just fine, it's just the lights which are the problem.

I've noted that the brake and directional controller box on the trailer wiring harness becomes very hot. I've checked and rechecked all connections and found no problems.

Any suggestions?

I just installed the OEM tow harness on the 2002 ML 500. The turning light and the braks lights are not working. When I turn on the parking lamp and headlamp, all the lights on the trailer lites up but the turning and brake lamp still don't work when I press on the brakes. Could it be the harness or ???