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hello, i have a 08 ML320 cdi that i have spent a lot of money on trying to get the trailer lights to work. i had a new SAM module put in, that did not work. at first it had power but the lights did not work, then it had no power to the connecter. now it has power but still not working, what is the problem?
it was bought and installed (not going to say who because i dont want to be rude) a mechanic, i dont know what he did with said SAM. is it a fuse in the wrong place?
it was bought and installed (not going to say who because i dont want to be rude) a mechanic, i dont know what he did with said SAM. is it a fuse in the wrong place?
What hitch was fitted?
The genuine factory fitted hitch connects to the rear SAM. This the needs to be coded in. If you don't do this when you retrofit it, then the SAM, and therefore the car, won't know it has been fitted.
It's possible to bodge the hitch socket direct to the rear lights, but it's never done properly.
If the trailer is a rental, don't ignore the possibility that the trailer wiring is fubar.
Post some pictures of the hitch and wiring to the SAM/rear lights.
On my '07 280cdi, I removed the aftermarket hitch fitted and bodged in by a previous owner and replaced it with the factory folding hitch from the facelifted W164. Rather than being crimped onto the tail light wiring, the harness plugged straight into the dedicated socket on the SAM. Five minutes with Entry and it works pretty much* as the factory intended.
*I say pretty much because trailer hitch option 550 on the pre facelift doesn't allow for the folding hitch release handle lock indicator even though it's wired in correctly. Doesn't affect operation, but I have to double check that it is locked. No big deal, as it's good practice to physically check it.
Factory installed hitch? U haul trailers require a special round adapter for your vehicle for the lights to work properly. U haul sells the adapter, at least they used to. I'll get a part number next time I'm near my w164. Also, the SAM, instrument cluster, and possibly central gateway need to be programmed by a dealership or someone with Xentry for the trailer hitch "present" Also may need a fuse inserted into the rear fuse box
Last edited by E55Greasemonkey; Nov 8, 2025 at 07:57 PM.
Whether the actual hitch is original or aftermarket, the wire harness to trailer connector should be. Nice plug on it connects to rear SAM.
as noted, rear SAM must be told there is a harness plugged in so a trailer can be detected and lights work. There may be need to also advise if LED.
It’s my experience that even though the trailer lights work correctly, a tester plugged into the connector may not.
when you have a working connection via rear SAm, you can receive dash messages regarding burned out trailer lights, and when your rear SAM detects a trailer is connected, it will cause Airmatic to not lower vehicle at highway speed as it normally does for better fuel economy.
The genuine factory fitted hitch connects to the rear SAM. This the needs to be coded in. If you don't do this when you retrofit it, then the SAM, and therefore the car, won't know it has been fitted.
It's possible to bodge the hitch socket direct to the rear lights, but it's never done properly.
If the trailer is a rental, don't ignore the possibility that the trailer wiring is fubar.
Post some pictures of the hitch and wiring to the SAM/rear lights.
On my '07 280cdi, I removed the aftermarket hitch fitted and bodged in by a previous owner and replaced it with the factory folding hitch from the facelifted W164. Rather than being crimped onto the tail light wiring, the harness plugged straight into the dedicated socket on the SAM. Five minutes with Entry and it works pretty much* as the factory intended.
*I say pretty much because trailer hitch option 550 on the pre facelift doesn't allow for the folding hitch release handle lock indicator even though it's wired in correctly. Doesn't affect operation, but I have to double check that it is locked. No big deal, as it's good practice to physically check it.
well the person at uhaul said "we just had new LED lights put on all trailers" so i dont know if it was done right
well the person at uhaul said "we just had new LED lights put on all trailers" so i dont know if it was done right
Did you have Uhaul install an aftermarket hitch with an aftermarket light harness? If so, go back to the Uhaul and demand them to make it right. None of us can help you in that case.
If you did install an OEM hitch, go find a Mercedes tech in your area. Your reply shows you don't know where to even start diagnosing the problem.
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