2018 E400 Coupe taillight harness
 

Hi Everybody,

I have a 93 300CE. My son bought a 2018 E400 coupe. It's interesting to see the two next to each other. Its A MB dealer STAR used car he got when a couple of year old. Car is spectacular but plagued with expensive problems. It's out of the extended warranty in a couple of months.

The newest is it now won't pass NYS inspection because the trunk mounted taillights are out. Dealer said harness is defective near trunk hinges. Dealer says if you wiggle harness the lights work so they cobbled something to get it working, but now won't pass inspection again.

Dealer says whole harness has to be replaced for $4500. Or there is a wire "healing solution" for $1100. I can't believe the the hatch harness on our 27 year old Jeep Cherokee works fine. Mercedes can't figure this out?

I'm pretty good at wiring and have wired a couple of complete cars, but I'm afraid to touch this. Can it be as simple as finding a frayed wire near the hinge, or am I going to get into some system controlled never ending nightmare? Or maybe the harness is pulling on a connection intermediately?
Bad ground?

Has anybody else run into this?

Would appreciate your thoughts.

Thanks!

Yes it is, uncover the wiring at hinge area to inspect. Splice whatever you find broke and tape/cover back up.

Unfortunately, it wasn't that easy. The harness idea came about because the dealer (Keeler Mercedes, Latham, NY) sent my son a video of a mechanic poking a stick in the trunk near the hing and making the lights work.

I think this is something different now. I pulled the trunk panels and wiggled everything I could find and found nothing. I tested one of the taillights with a PowerProbe and couldn't get the lower brake light bar to light.

Three of the five brake lights don't work. I think all of them have moisture in them.
It doesn't make sense to me that three $300 taillight units would be bad at the same time. I think I like old fashion bulbs better!

I did find a factory manual download for $15. 7,650 pages! and it doesn't have any of the supplemental pages.

Looking at the the wiring diagram, it looks like everything runs from a SAM module in the trunk. Researching this shows that the connection can corrode, but wiggling the plug had no effect. But the SAM module seamed really hot to the touch. I can't imaging it drawing enough power for LED taillights to get hot

So I guess I'm out of my depth with this thing.
My son is calling Keeler and of course it is out of warranty this week

Thanks for any advise.

I would remove the plastic protective cover and try to inspect the wiring in the hinge area.

Yes we did that but it didn't have any affect.

Thanks

Finally got the dealer to repair it under warranty. It's amazing the different answeres you get by talking to the right person.

Dealer replaced three taillight units and a bad harness connector.