gbigpapa

I just installed a trailer brake controller and had to bring the wiring from the back up to the front. I took a bunch of photos along the way. If you can send me a photo of what you have I can check to see if I have any photos that match or try and trace the wires to help you out.
-George

gldave

I'm also looking purchase and install the OEM trailer hitch. Any suggestions for where to get a good price / salvage?

jonathankreb

I hunted around and found one at the following link was the best price I could get:

http://www.oediscountparts.com/partl...769&startrow=1

I was leery about buying a salvage hitch as the earlier models (2007ish) had a recall and needed to be rewelded/beefed up. Was also worried about getting all the parts with a salvage hitch (there are frame strengthening bars that are part of the assembly.

The only other option I found to get the full towing capacity of the GL was with Execuhitch. The price was comparable, but the shortcoming I saw is that because of their unique design, you don't have the options you have with a more conventional hitch, ie. the ability to use weight distribution hardware, etc.

bajatammy

Tried to set up my 2007 MB GL450 to tow a camper that I just purchassed. On fuses chart fuses 70,71and 72 should be set fot the trailer hitch but those were not installed at all RV Dealer could not figure out why no lights on the camper when connected to the car's factory installed 7 prong outlet. Only light that was working was clearance lights. No turn signals, brake or running lights were working. Also electronic brake controller could not be paired either. When electric outlet on my MB was tested seamed like 5 of 7 prongs had constant power except turn signals and brakes (I think that is what dealer told me) Anyone have any ideas what should i do.

KrustyKustom

I have a 2011 GL350 that I use to tow a 30' Airstream and I had the same issue when I first hooked it on the trailer. I even had it back to the dealer and they said it was all good. What you have to use is a LED adaptor that goes in line of the 7 way plug. It effectively allows the rear signal acquisition module to recognize the trailer load. When the trailer lights are activated the lead to the trailer brake controller will work.

etrailer sells the LED adaptor, theirs says for VW, Audi and Porsche but its just the standard 7 Pin.

bajatammy

I also have another problem though.....if I turn on turn signal for example, all five pins get power except brake controll pin. Same happens if I press brake pedal. If I hook up the trailer only clearance lights comes on nothing else. I have not seen any messages on dashboard to say bulbs not working or anything like that, like some people have issue. Just trying to give some more details for better understanding. Thanks Krusty Kustom.

jonathankreb

First question is, does the trailer you are trying to control have LED brake and turn signals? If so, this is very likely your problem. I went round and round futzing with my system when I first installed it, and it just will not respond like you would expect a "normal" vehicle to. I found that putting a meter directly to the plug yielded oddball responses, like you describe. It is because the vehicle has to recognize that there is a trailer behind it (due to the resistance of the brake and turn signals), before it will even send out the proper signals. I ended up replacing my SAM, though the original was probably fine, and then taking it to the dealer, where they "reprogrammed" the SAM (which probably didn't need to happen either). I finally figured out my problem when I hooked up a known-to-be-working set of conventional trailer lights, and magically, all worked perfectly.

good luck!

studioab

Guys,

it seems I'm in the same boat

My 2011 GL450 came with OEM UHAUL hitch. The previous owner didn't care about towing, he just used the hitch for the bike rack, this is why wiring wasn't done.

The UHAUL hitch has 4 and 7 pin connector installed but wires are not connected. My popup trailer has 7 pin connector and electric brakes. I called MB and asked for the original hitch harness. They sold me P1644406434 also they checked VIN# to make sure that my SAM module doesn't need to be replaced.

I connected one end to the rear SAM, fixed the ground lead and plugged in power lead to the fuse box (brown socket).

The green connector for electric break control is not plugged in because I'm going to use RF prodigy brake controller.

The problem I have right now is that UHAUL connector has only 7 wires coming out and I don't want to spend another $90 for the same connector but from MB also I don't have time, I want to go camping

This is what I see when Engine is on
Brown - Ground
Red - 11.98v
Gray/Black stripe - 3.89v
Gray/Yellow stripe - 3.89v
Black/Green stripe - 10.78v
Black/White stripe - 10.78v
Yellow/Red stripe - 0 (this is the wire for the EBrake this is why it's not hot)

My ask for anyone who has GL450 with original towing package, pretty please with cherry on top, send me a wiring diagram of the MB 7 way connector. You probably will need to use tester to ring each pin

here is MB connector with 7 pins that I have. Color schema doesn't make any sense to me and I can't match it.


It has to go to the standard 7 pin connector like this



I'm buying beer to you

N_Jay

Put a test bulb (an old turn signal bulb works fine) between each of the unidentified lines and ground.
Turn on and off the running lights, Hit the brakes and try the turn signals, and you will identify each line.

studioab

I did. It doesn't light up. The V dropping to 0 on the wire when I connects the bulb. It seems I need to somehow put MB computer into "trailer" mode and I don't know how it detects if trailer hooked up.

I checked the trailer ground and car ground. Connection is good.

Any ideas are appreciated.

wally AMG

I know you got the harness, but did you get the MB female socket? the wiring end you show in picture fit in this socket

http://www.ebay.com/itm/Mercedes-Benz-Trailer-Hitch-Plug-Socket-Genuine-X164-GL-GL320-GL450-GL550-/190738884466?pt=Motors_Car_Truck_Parts_Accessories&vxp=mtr&hash=item2c68ec6772
Dealer need to program your rear SAM to recognize trailer hitch (with SDS) not just for the lights, this helps with your airmatic system and brakes

studioab

No, I didn't order it. I'm looking for help with the wiring diagram to connect Mb harness to the uhaul 7pin hitch connector.

N_Jay

Maybe it needs to see bulbs on multiple leads to trip on.
Does the "red" line light the bulb?

studioab

Yes, it does. I tried two bulbs as well.

At this point I think my rear SAM has to be reprogrammed for the hitch.

wally AMG

So you cut the wires and tap to the uhaul hitch connector?

studioab

yes.

N_Jay

How did you decide which wire to where?

studioab

I got help on this thread https://mbworld.org/forums/gl-class-...ml#post6053528

wally AMG

Rear SAM has to be reprogrammed for the hitch.

studioab

Saga continues ...

They reprogrammed rear SAM this morning. 1 hour or labor ($135).

I came back home, this is what I got so far:

1. Connect trailer to MB and start engine.

2. MB recognizes the trailer. I see the message saying that Blind spot assistance isn't working. Which makes sense. Good. This message wasn't there before. Let's move on.

3. I turn on headlights and I can see tail lights on trailer. Great.

4. When Left Turn is on, message pops up saying that Trailer Left Light is malfunctioning but I see left turn light flashing on trailer.

5. Same thing with Right turn. Message pops up but right turn light is flashing on the trailer.

6. On brake I see message pops up that right and left tail lights aren't working and now all lights including tail lights flashing.


I checked all the bulbs and I even replaced them all. They are all working properly when I tap 12v on the pins. My friend has Toyota track, we tried to hook it up and lights on my trailer are working just fine.

I desperately need help.

Thanks a lot.

N_Jay

Are they LED lights on the trailer?


If so, they don't pull enough current to keep your MB happy.

studioab

No. Its an old school ('02) popup trailer.

N_Jay

Check the bulbs. Mine showed an error when one of the sockets had a little corrosion.
I did not check to see if the light was working or not.


Someone could have put in smaller than normal bulbs also.

studioab

I did. Cleaned the sockets and replaced bulbs.

KrustyKustom

Did you test this with the trailer connected via the hitch ball? I know it is simple but trailers use the chassis ground, it has to connect and sometimes has to move a bit if corroded hitch.

Just checking!