Here is one from out in left field--AND I can for the present use my White Knights manually when I really need them at present----------------

How about connecting to the rear fog light (which I never use) to the White Knights ? It would be a manual turn (fog) on at the dash for the back ups but compared to driving forward I dont always back up

JP

I have connected the WhiteKnight light unit through a wireless power switch (LOGISYS RM02). In this method whiteknight power switch is always at on position and wireless key fob will be used to switch on/off whenever needed. Now no issues with the blind spot warning.

Well.......that's at least a measure of success! How unfortunate that we cannot get something in a normal "put it in revearse-lights come on" manner!

I think this is going to be a much easier mod if you tap into the existing backup light circuit, and then use a 12V signal to the backup lights to trigger a relay that powers on your add-on backup lights. I don't think this should be too hard of a mod.

If you tell the GL computer that a trailer is connected, it puts the truck into towing mode. Your blind spot sensors turn off, you can't raise the air suspension, it pays attention to whether the trailer brake and turn lights work, it probably does other funky things in terms of the ride profile - like turning on the anti-trailer sway functionality. On my X164, it's also looking for the proper resistance levels on the brake light circuit - it actually sends a power pulse to the tail lights and is looking for the expected resistance of an incandescent filament. (Which is why putting led bulbs in your trailer stop, turn and tail lights freak out an x164 - it sees them as open circuits)

If it would be helpful, I can test on my GL to see whether it's plugging in a trailer to the rear 7-pin connector, or plugging in a brake controller under the dash, that tells the GL computer that the truck is connected to a trailer.

But like I said - I think that you won't like what happens when you do this in terms of your daily driving..

Guys,

I found this thread and 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.
http://c1552172.r72.cf0.rackcdn.com/290666_x600.jpg

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

http://www.tacomaworld.com/forum/att...g-7pinplug.jpg

I'm buying beer to you :)

7 blade trailer hitch connection
 

I have a 2014 GL with the trailer hitch and 7 pole connector wiring, and I checked underneath. This MB connector you show connects to the MB female 7 pole connector which is located to the left side of trailer hitch. From wiring trailers, I can safely say the MB female 7 pole, with this connection to the MB harness is probably an MB proprietary part, and you will have to get it at Mercedes. With luck, the MB female connector can be mounted right on your U haul hitch. Once it is installed, you cannot use a voltmeter to check it out--other people have tried this, and due to computer control of this wiring, this does not work. Instead, I have successfully used a Curt 58270 7 way rv blade tester (available at Amazon) to verify the 7 blade MB female plug is wired up correctly and working the way it is supposed to. I would get one of these female connectors at Mercedes, try plugging it in, check it with the Curt tester, and if works OK, then figure out a good way to mount the connector on the U Haul hitch.

I thought about this a little more, and if you want to save getting a Curt tester, you can try plugging the connector directly into the 7 blade trailer connector, and see if the turn signals and running lights work. If they do, you will be good to go, and you can mount the connector on your UHaul hitch. Good Luck!

Ed - thank you for advise. That's what I already tried but since I don't know what wire goes where MB won't recognize the trailer/tester.

Did you try to unplug your harness from 7 pin hitch connector? There is a little red plate that needs to be pushed out to let the plug out. There you will see 7 male pins. I would really appreciate if you can ring them out so I can fill the rest of the MB connector wiring diagram.

Here is what I figured out so far.

Thanks a lot in advance.

I unplugged it to check on it, and verified it was what you were looking at. Your problem is that MB does not recognize your trailer with your U Haul hitch connected and these wires coming in. I don't pretend to understand how MB has rigged this wiring, but since the MB hitch works fine with a 4 pole connector, which is running lights, rt turn, left turn and ground apparently it needs to sense connections between these before the power to the hitch connector is turned on. I can try checking out mine with a continuity meter and will let you know what I get. I'll have to wait to do this, the vehicle is parked outside and we are in the middle of a thunderstorm. I'll probably do this tomorrow.

I'm going to try cheating MB computer with the "ground" trick and see if it works, but looking forward for your reply. Thanks a lot.

I tried grounding the ground pole in the MB 7 pole connector, and this does not turn on power to the hitch plug. As I said earlier, it seems to sense continuity between the ground and one or more of the other poles, or some combination of this and a ground. Whatever it is, it runs fine with a 4 pole adaptor, but as others have found out, it will not work with a one pole ground to backup light setup (the standard in add on back up lights). I've been meaning to try to fool it with some resistors between the turn signals and the ground, but this is one of these "rainy day" jobs I have not gotten to.

One other thing, if you have a problem, such as a left turn trailer bulb burned out, it will sense this and tell you about it.

One final thing, the Curt tester I mentioned uses a low wattage LED display, and the hitch wiring works well with this. So, apparently even a very high resistance connection will activate the hitch plug.

I tried using 12v bulb as "resistor". Every time I connect it the one of the unidentified wires and the ground current drops from 3.89V to zero and bulb doesn't light up.

My trailer lights work just fine, I tested them on other car. I don't understand why you think curt tester can activate hitch plug but not trailer.

I doubt that German engineers are that "smart" to put in some kind of technology to detect/recognize the original harness plug in the hitch connector :)

I guess you've never tried to replace a burnt taillight (incandescent) on a recent MB or BMW with a LED replacement? ;)

MB trailer wiring
 

Apparently, there is some misunderstanding. What I've stated is that the Curt tester apparently tells the MB trailer plug to turn on power. 4 pole trailer lights do the same thing--the plug works well with a 4 pole adaptor. But, just connecting the grounding pole in the plug to a ground will not turn it on. Similarly, just hooking up the back up light pole through a resistance to ground will not turn it on. It apparently requires some sort of circuit, which apparently can be very high resistance, between the turn signal poles, the running light pole, and the ground to turn the hitch wiring on.

In any case, tomorrow (it is already 9 PM here) I'll try to send out a wiring continuity diagram between the MB plug and the MB 7 pole hitch female plug.

Thanks a lot, Ed. Looking forward for it.

Just in case, this is the rear SAM that is installed in my car

ZB: A 164 900 54 01
HW: A 164 545 75 16
SW: A 164 902 57 00

Do you think I might need to ask dealer to program it for the hitch?

Wiring connections for the Mercedes trailer hitch
 

These are enclosed in an PDF attachment. I pulled the trailer plug assembly off, and checked for continuity between the blade connectors on the trailer plug assembly and the 7 trailer plug prongs. Both of these images are taken from the front of the plug, peering into it. If you have any problems reading this, let me know.

Ed - you are my hero. Thanks a lot for doing this.

Great, this is what I had before and this was correct :)
- (f) ground lead from MB goes to pin 3.
- (e) ebrake yellow/red from MB to pin 4
- (c) 12V red from MB to pin 6

Rewiring the rest:

- (a) right turn black/green to pin 5
- (g) left turn black/white to pin 2
- (d) tail light gray/black to pin 1
- (b) reverse gray/yellow to pin 7 center pole

Will post results shortly.

With your great help, I've done everything I can at this point.

MB still isn't recognizing the trailer :(

I think I should ask dealer to reprogram the rear SAM.

Here is the voltage when the engine is on. Do you have the same?

Trailer plug wiring voltage with the key on
 

Here are the voltages I got with the key on:

(using the same pin numbering system I used in the response before)

1 1.5v
2. 1.5
3. 0
4. 0
5 1.5
6 12v
7 0

I used a Fluke meter, so the difference in low voltages may be due to meter impedance.

It sounds as though you will have to do some more checking on what it takes to turn the trailer hitch plug "on".

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.

It sounds like their reprogramming was faulty. Even though power is now going to the turn signals, and they show power usage (circuit continuity) the program is telling your dashboard readout that lights are not working, that there is no continuity there. So, getting the programming fixed is the only solution. Incidentally, turning on the emergency flasher, which flashes both turn signals, is a good way to check the brake signal (it is basically an intermittent brake signal) without having somebody standing behind the trailer. while you apply the brakes.

From Invoice:

"CLIENT REQUESTED (PROGRAM REAR SAM) HE HAS ADDED A TRAILER AFTERMARKET HITCH AND NEEDS THE SAM PROGRAMMED TO WORK WITH HITCH

CODED CENTRAL GATEWAY AND SCN CODED REAR SAM-RETROFITTED CODE 550 INTO CODING STRING TO ENABLE TRAILER LIGHTING CONTROL.

PERFORMED FUNCTION TEST WITH TRAILER LIGHT TESTER AND FOUND LIGHTING WORKS"

Honestly I don't understand how programming could be done wrong. Here is the code http://www.micro-tronik.com/learning...-164/rear-sam/

What do you suggest I should tell them? I even don't know what tester have they used to make sure SAM is working properly. They can always refuse to do anything because it's aftermarket hitch.

When emergency lights are on, the left/right lights on trailer are flashing with error message.

Thank you for your help.

Happy end!

Attachment 290155

See attached for details. In few words, they ended up replacing Rear SAM module. Thanks God for MB warranty :) The estimate was ~1.5K for the diagnostics, parts and programming the new SAM.

I appreciate all your help.

Glad you finally got it fixed. I don't know why MB has such a complicated way of handling power to the trailer plug. Most other manufacturers just rig the trailer plug with the same controls as the car lights etc, (but with separate fuses) and let it go at that. You do have to check the trailer lights manually, but it saves a lot of time and frustration compared to trouble shooting the MB unit. And, with LED trailer lights, problems with burned out trailer lights are minimal.