Help! Trailer lights not working and need to move a boat...
 

'05 ML 350. I installed my trailer hitch today, I used a draw tite hitch for the ML and purchased the factory wiring harness and factory 7 prong plug.

As per manual I installed and connected the main connector to the brake module and turn signal inicator plug. The lights do not come on on the trailer... :(

The manual shows on extra connector, which does not seem to go anywhere and the part I received from MB does have two extra connectors next to the brake and turn signal connector.

Am I missing a module? Is there maybe a fuse I need to install?

I am about to go and pickup my new boat and this is all keeping me from going. Any help would be great.

Thanks, Sab.

Sab, hard to troubleshoot your problem, my trailer light problems have always been GROUND connection problems. If your picking this boat up during the day time, I have done that with no brake lights, just to get it home. Never has been a problem. Your choice, just a suggestion..

After completing the installation instructions included in the trailer hitch kit, please insure that a 25-amp fuse is installed in position F18 in the fuse box (F1).

I don't know if above is the souce of problem or not.

thanks,
the lights seem to work, but no indicator or brake light.
I placed a fuse in 18 and no change.

Searching the forums I found a post suggesting a relay is needed somehwere.

Is it possible the two empty plugs on the new harness need some sort of relay or modulator?

regards,
Sab.

anyone has any info if I need a relay somewhere?

Just a thought, it's hard to see when backing up a trailer with a ML. If possible, I try to open the liftgate before backing a trailer. Good luck with the light issue.

OK, it is finally working.
It seems that the parts guys are not familiar with the tow package parts. Since I purchased the hitch elsewhere and wanted only the harness and any parts needed to get the electrical part to work, they had no clue what parts to sell me.
Repeaded call always went in the direction of ... "well, if you are installing it yourself, you are doing something wrong" or "the problem is you are using a draw tite hitch".
I escalated the issue to the parts director and he got a tech involved. Tech stated "all you need is the harness and plug it in..."
Well, I pointed out that the manual shows a piece, looking like a module with a clip on it and my harness had only an empty plug.
The parts director was so kind and made some phone calls. He got me the missing module and it now works. He actually gave it to me for free. :)

Just thought this might be helpful for someone that expiriences the same problem. The harness needs a seperate brake and indicator module to work.

regards,
Sab.

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 ?

Sounds like you have the same issue then I had. Does the harness have the brake and turn module plugged in?

You got something for free from a MB dealer. Quit pulling our chain.