Millbrooke

2009 ML320 CDI with factory wiring kit installed but trailer lights not working. Wiring all ok from plug back to SAM in rear. This has been checked by an auto electrician.

Is it likely to be a SAM set up issue.....ie a dealer fix?

texterted

You may need it to be enabled on STAR diagnostics.

mrfixit51

I have the same problem, same model and year of vehicle. No parks or backup lights. Still not sure if the brake control works. Have left and right signal and +.

Rightleft2

I know this is an old post but did you ever figure this out? I am having the same issue (Have left and right signal and +)

Maj. Dundee

Please read steps 24 & 25.

Rightleft2

Thanks I appreciate the response. So I had the dealer replace my SAM with one that has the plug for the hitch wiring harness and asked them to program the new one so I can tow. Can I assume steps 24 and 25 were done or are these steps separate from programming the rear SAM itself?

Maj. Dundee

In your original post you said nothing about the dealer being the one who installed the the rear SAM.

If that is the only thing they did, then nothing will work because they did not perform any of the other steps. Did you read all of the steps?

Rightleft2

They installed the sam and programmed it. I installed the hitch, harness (interior for the brake controller etc. and the one going to the hitch), required relays, and connected it all together.

Maj. Dundee

Well something must have gone wrong on either your side or theirs.

Rightleft2

I went to the dealer again and had them recheck their programming and do some troubleshooting for 3 hours with no luck. Next steps are they replace the SAM which is going to cost me more $$$ I'm not sure I want to spend on my weekend vehicle.

I'm debating cutting my losses and going with an aftermarket kit - is anyone here aware of any downsides to that (besides hacking into factory wiring)? I have the OEM hitch so I can physically tow my ~4000lb trailer, I don't have airbag suspension, and IIRC my 2008 ml320 doesn't have any stability control stuff. Is there a benefit to my transmission or anything else having the rear SAM be aware of a trailer being plugged in?

Maj. Dundee

Every veh. has ESP.

The answer to your question depends if everything is working properly. Do the brake lights work on the trailer?

Rightleft2

All the lights work on the trailer when hooking it up to friend's trucks.

When I use a tester with and without a led adapter from Curt I just get 12v from the plug on my hitch on my vehicle.

Maj. Dundee

Please explain this sentence & who knows what Curt is?

Rightleft2

Curt (the popular company that makes gear for towing etc) has an adapter for trailers (or testers) with led bulbs that from what I understand is commonly used for German vehicles when towing. It tricks the car's computer into not triggering a warning that the bulbs are burnt out as (from what I understand) their voltage is too low for the car's computer to register as a working bulb. I was told that may be an issue as well but that's not the case here.

My question is what am I losing out on if I forgo the SAM and use an aftermarket 7 way wiring kit.

Maj. Dundee

So I think what you are saying is the hitch works on your friends car but not on the ML. I would have no idea why it won't work on your ML since it is an aftermarket component.

LUDONNA STUDIO

any update？I got the exactly same issue here，dealer ask me to change the Sam，IT not worth to do that. did you find any bypass sam aftermarket module？

LUDONNA STUDIO

any update there，I have the same problem here，dealer wants to replace the Sam

Feliks Soe

Same problem here also. No power to the trailer. Some very popular case on ML and GL.

Tsumi

Need way more information than that. You're better off creating a new thread on what the symptoms are and what you've done to troubleshoot.

As for the things missed out on by bypassing the SAM: trailer sway control, altered gear programming (holds lower gear longer), does not lower at highway speeds if equipped with 4 corner air, stiffer shocks if ADS equipped, and brake bulb out detection.

Feliks Soe

Thanks for answering first.
I will make a new thread on this topic as you mentioned.

Carcheologist

FWIW on our 2010 ML350 it doesn't like our old trailer and it's crappy wiring. I get "trailer light burned out" messages unless I use an LED adapter in line, then it works.

Feliks Soe

My one is not functioning new idea.

Hussnainh8

Hello guys

Did anyone find a solution to this as I have same issue on my ml320 2008. Tried a trailer light board (no lights), tried my old trailer which has standard bulbs (no lights) and then I tried my new trailer which has dynamic led lights (from eBay, getting power to indicators so sweeping indicators but they are always on and I can't stop them without disconnecting the 7 pin plug. No tail lights or brake lights working on trailer just the sweeping indicators constantly on and can't turn off without disconnecting plug. I am imaging its a issue with my SAM but want to know definitely before wasting money. I am also wondering if there is a alternative solution such as to buy a bypass box of eBay and rewire the trailer socket to my tail light? Would that work?

Feliks Soe

My resolution went to be- new Rear Sam. The worst what i been thinking.

Carcheologist

Have you tried one of the adapters for LeD bulbs to trick the vehicle into seeing them? If you’re in Portland, Oregon you’re welcome to try ours. Or buy one off Amazon and return it if it doesn't work.

you could also try just tapping into the rear light like an older car, but the computer might mot like that and cause issues.