simandang

So the left taillight doesn’t work. I replaced the bulb it still doesn’t work. I bought new facelift style LED taillights and it still doesn’t work.

The turn signal works, brake light works. Both functions work on old and new taillight. Just the running light does not function.

wiring looks good no corrosion.

Any knowledgeable members have any tips or advice on where to look.....

streborx

Does "wiring looks good no corrosion" include the bulb's socket ontacts?

Floobydust

Check the wiring/connectors carefully for corrosion. Are you getting a "bulb out" message? Smells like it might be a bad rear SAM to me. Get the standard bulb working first. LED replacements are a trip down the rabbit hole even when everything else is otherwise working.

simandang

Interesting solution. It ended up being a bulb that was faulty that was causing a short or some sort of weird problem.

I swapped the bulbs over to test and the right taillight started doing the same thing the left was doing.

so I focused on the new lights

I got the facelift LEDs taillights working perfect (they look awesome). Unfortunately the screws they sent do not fit to secure the light housing.

Hopefully I can find appropriate screws that fit.

streborx

Was the original bulb one of those wedge types that lack a brass bayonet base? The wedge base lamps have contacts comprising only wires emerging from the glass, and it take very little for these wires to twist, bend and break.

simandang

So even more funny stuff, I thought I had them wired perfect but turns out some extra lights were turning on with the turn signal and just in general they were doing weird things.

I realized back in 2018 I had gone to the dealer for a similar issue for the taillights which I had forgotten about. I looked at my paperwork and it seems Mercedes installed some sort of extended “harness” and some extra wires that were doing absolutely nothing and a few that were plugged in random spots.

I took that extra harness and wires out and threw them in the trash. I made a few diagrams and color coded each wire from the original harness and my new tails and one by one did process of elimination to get everything to function. It took a few hours but everything is working perfectly now.

Also got proper screws and everything fits snug and perfect.

If anyone happens to get these style lights which I have attached feel free to PM me I can send you the diagrams I made which will save you a lot of time. The instructions that come with the light are not correct.

Floobydust

WTF kind of dealer did you go to? Did they try and install a trailer light harness (not sure of the year of your truck)? If a trailer harness is not applicable to your truck, you should tell the service manager that, while it might be legal in your state, they really shouldn't smoke dope on the job.

streborx

This is a bigger problem than most people realize, and by itself is reason to learn how to do maintenance yourself.