I just installed the OEM tow harness on the 2002 ML 500. The turning light and the brake 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 the 7pin to 4pin converter. I lost the original 7 to 4 pin converter so I bought an after market one, could that cause the problem?

 

Did you install fuse 18, front fuse box?

 

It does not come with one, but I will check. If it's missing the fuse, shouldn't all the trailer lights not work? if I turn on the parking lamp, the trailer lights ups, just when I step on the brakes and turn signal don't work.. Thank again

 

I bought that $100 harness and for 3 years I have only had the lights on the trailers I have pulled. No brake lights, no turn indicators.

I only drive in day time and turn on my parking lights when slowing or stopping to warn drivers.

I wish I had saved the money and had it wired spliced to the tailight.

 

it worked before but I think I figured out what may be wrong with it. I believe it may be the 7pin to 4 pin converter plug. I got an aftermarket one and the pin layout is a bit different.

 

ok, it's not the converter, I guess I have to replace each piece of the entire harness one by one to see which one is not working.

 

Did you install the fuse like Later stated? The ML be default does not have that fuse installed and the trailer directions fail to mention it. Check the fuse before hacking your wiring. Mine did the same thing with only parking lights before I installed the fuse.

 

Do you mean the #15 and #18?