I am attempting to fit my Prodigy brake controller to our GL am suprised to find no wires present in drivers footwell for picking up the brake, brake output to trailer and power. I found the thread at benz world and followed the links to the MB bulletin. I am suprised that a $60k tow vehicle may need an upgraded SAM and custom wiring to fit the unit. A call to the dealer seemed to suprise them and has not been returned yet. Anyone successfully fit one to the GL yet. Thanks to all who may repsond.

 

I'm surprised to hear that the GL can't control trailer brakes. I was under the impression that having the round seven prong plug allowed such a control. I tow my motorcycle trailer often, but it has a flat 4 connector, which I use with an adaptor, and since it's a single axle trailer, no brakes are required on it. I wonder if MB forgot the all important fact that to tow the 7500 pounds our manual says we can tow, a tandem axle trailer is required, and that tandem axle trailers have electric brakes at the very least. Please share whatever information you can when you get your reply from the dealer.

 

Dealers shop foreman admitted he did not the specific location of the brake controller connection that was supposed to be wrapped to harness near rear SAM, he said it could be anywhere on car. I am just going to install my own harness and terminate it to fuse 71 that was supposed to feed the stock connector. I think the vehicles have gotten a little complicated for those who are supposed to know them best.

 

My 99 ML320 had a service bulletin that helped with the connection to a brake controller. Basically you had to cut a wire in the back of the vehicle and that allowed the brake contoller to modulate the 12V brake signal.

Finding that wire and routing 10amp (or was it 30) wiring was all that was needed.

This integrated well as when I used the brake controller manually (with the switch I could reach from the drivers seat), the brake light went on and disconnected the cruise control.

 

I just spent three days going round and round with dealer and two hitch places to get my horse trailer ready to go.

No brake controller wires running from back to under dash, so hitch place had to run them when they put the Prodigy in, and also when dealer installed the hitch ($2k), they didn't program the computer to recognize the lights and took two trips back for them to figure it out. (plus one other because the back hatch wouldn't open after they finished).

The most annoying part of the whole thing is that they advertise this car towing houses and boats and whatever other giant contraptions, and then throw their hands up and say "oh, we can't support a brake controller and if you put one in then your on your own". The whole reason I bought this car is for the trailer and its promised towing capacity. Pretty ridiculous.

 

Did anyone ever get more information on connecting a brake controller to your GL 450? We just bought our Pewter GL450 Saturday (and am thrilled with it)and when I asked my salesman about a brake controller, he said he thought it was not needed and would automaticly work since it has a 7 prong connector. An experienced trailer person knows that that is not the case and can be outright dangerous if not deadly. Even Dodge Vehicles come prewired for a brake controller so certainly a Mercedes vehicle rated at pulling 7500 lbs. should be prewired for a brake controller. We pull a four place snowmobile trailer (often on icy roads) and trailer brakes are an absolute necesity. Any help or suggestions on having a brake controller installed would be greatly appreciated.

 

See this link http://www.whnet.com/4x4/pix/164_Brake_Controller.pdf referenced from this page http://www.whnet.com/4x4/towing.html

 

I figured out how I was going to fit my controller the quick and dirty way if it comes down to it. I figured I would see what the dealer could do during my 1-3k checkup, i dropped the gl off tonight and printed up the star bulletin showing the connector that is buried under my sub-woofer. I authorized 1 hrs. labor as a teaser so they would at least try to help me out. I told them to just remove the R rear panel if they choose not to pull the sub and i would do it. I also had a bad 3rd row switch and an airmatic system that levels and farts each time a door is opened.
If worse comes to worse i will just use fuse 71 for power and the center brake light as the trigger and just hook everything up myself but I let them know I would prefer to use the MB connector and that the car is sold as a capable tow vehicle so additional cost/parts and programming is unacceptable. I should have an update tues.

 

It is truly upsetting and misleading to advertise that our vehicle can practically tow a house and it doesn't have the capacity to operate electric trailer brakes. From reading the above posts and the pdf file from Wolfgang's ML site, it seems like the brake controller was a total oversight. Anyone needing to tow a large trailer would have to go though the ordeal of having the controller installed, and this is a pandora's box itself, judging from the "expertise" our dealers' service techs have. As I mentioned in my original reply, I only tow a motorcycle, so trailer brakes aren't indicated. However, I too bought this vehicle for its towing ability, and now I feel very misled. If I get a multi-bike trailer with tandem axles, I'll be dead in the water. That's just not fair. For this kind of money, the trailer brake should be standard. Thanks for letting me rant.

 

JJM, thanks for posting the links.

One just needs to find a mechanic who is familiar with the towing kit. Here's a post by DR.DIESEL who installed one recently in a GL450. Folks who have questions might want to post a followup in that thread. I'll also include a DR.DIESEL link on my info page. MBUSA is not yet all that clueful when it comes to towing...

http://www.mercedesshop.com/shopforu...6&postcount=10

 

UPDATE:
I challenged the dealer to find the connector during the 1-3k checkup and even authorized 1 hour labor to give them a head start. I don't think they could find it (did'nt try to hard)so they gave my wife an estimate of 3 hrs ($395) to locate it and she really let them have it. So bad in fact that when I called to checkup on the status they said they located it and routed it to the rear fuse access panel for the 1 hr. charge.
They said they located it under the sub woofer and behind the rear sam unit. It has a green connector just as shown in wolfgang's post. I think you can reach it by pulling the pins and pulling back the right side of the spare tire well to reach it. Now I just need to pull the wires to the front and I am all set.

 

here is the GL with trailer attached, I did not mount the spring bars as I was just towing around town. The airmatic just picks the car back up to standard height after trailer is placed on it. I lowered my GL slightly to allow the rear hatch to open without hitting my garage door and eliminate the stink-bug look.

 

Thanks to LDH's post, we finally found the connector just where he said it was. You have to pull the spare out and remove the side panel to get under the subwoofer. It was tucked way up inside. Now we have to route wires all the way up to the dash. It's a real shame that you have to go through all of this just to hook up a brake controller. Does anyone know a way to get to the right people to have them address this problem? I was told by the dealer that it's ready to tow 7500lbs. Just plug in the seven prong connector and go!Maybe it is going to take a serious wreck from someone hooking up a 7500 lbs trailer with no brake controller before Mercedes Benz addesses this serious problem.

 

I'm glad I didn't start poking around under the dash in the front. In another post someone said they found it in the front behind the drivers side kick panel or something along those lines.

Does anyone know what the 4-pin connector looks like or better yet, have a link so I can buy one quickly?

 

You seem to have posted to an ancient thread, but I battled all last year to install a controller on my 2010 GL350. Not willing to pay a dealer $2k for what should be a simple hook up on a truck that came pre-wired with a a 7 pin connector. Here is what I learned.

In the right wheel well near the fusebox there is a small green connector that "apparently" is to be used for an electric brake controller. There is a place on the fusebox to plug it in. However, no one from Mercedes could find the other end underneath the steering wheel. Despite pulling apart half the dash. It may be there somewhere, but...

As an alternative, consider a Tekonsha RF. It is not hard wired under the dash. The main control unit mounts on the trailer tongue, and then you have a remote unit plugged into the 12v outlet near your dash. It is a little more complicated to "pair" up the remote with the trailer controller, but you have the advantage of taking the controller with you no matter what trailer or tow vehicle you are using.
I hope that helps.

 

I had a Tekonsha prodigy P3 installed in my 450 GL. What a nightmare and frustration and it costed me over $ 500 until it was finally working.
Now I traded my 2010 450 GL against a 2015 350 Gl bluetec and I decided to
use a Tekonsha Prodigy Rf to control the trailer brakes. Wow, no wiring needed and the installation costed me nothing. Just 4 screws in the trailer frame and the rest is plug in. This is the way to go! It works fantastic. The display can be installed on the dashboard and pluged in the cigarette lighter. The controller is fixed to the trailer frame with 4 screws. All you need is a 7way plug on the car and on the trailer. You also need a LED bypass adapter so the mercedes can control the LED lights. I just drove from Tucson to Denver with my 7000 lbs toy hauler and it worked great. I don't understand anymore why so mani MB owners mess around with wiring and under dash fitting of a brake controller.

 

I did my 2008 320 CDI, I was able to find the green connector above the drivers kick panel, near the parking brake, like in Wolfgang's post. Then you have to get the correct MB Mating connector and pins to pin up the cable to your aftermarket Brake Controller. Somewhat of a pain, but not worth paying $2K to the dealer to do it.
For those looking to tow closer to the max tow rating, read the "Towing a big load?" thread and consider re-enforcing the hitch if you have an older (2007-2010?) GL. The newer GLs seem to have fixed the weak welds issue on the OEM hitch.
Good Luck.

 

The Touareg, Cayenne and the Q7 have the same kind of setup going. The factory just leaves a pigtail behind the driver side kick panel and we have to buy the adapter harness that translates from the pigtail to the Tekonsha. I actually did it myself on my Touareg. However, I have a feeling it will be more involved in the case of the GL. If someone could post pictures from the underside of the driver kick-panel to show the connector, it would be helpful.

Probably because:

1) They already have a brake controller and don't want the hassle of selling/repurchasing/wasting money.
2) They don''t trust the RF mechanism. Not saying their distrust isn't misplaced, just that people tend to view dependability differently when anything wireless is involved in towing.

 

Yes, the bulletin T-B-31 19/07d explains the process, but not very well.

It implies that the harness from this rear connection to the front driver footwell will be present, but I think this may be the case only on cars factory fitted with the trailer package.

My fairly early production car was not factory fitted and the dealer fitted the hitch and hitch wiring upon my purchase. Turns out they did not run the wiring to the front for the brake controller (and there wasn't any there factory fitted), but indeed the connector for this wiring is present near the rear fuse block ... I assume because a new SAM was fitted when hitch was installed.

Here's the answer to the hard part: the part number for the rear-to-front harness is 164 540 69 13. This is a little difficult to find in the parts system (EPC) and it's not listed in group 31 or 54 but in group 99. $36 msrp, $24 + freight ordered online.

I've obtained this harness and for sure the connector will mate with the green connector floating in the rear compartment, and the green connector at the other end does indeed mate with the connector block that the DTB lists for making a harness to the controller. It's all color coded the same green and the fuse holder that's part of the harness is also color coded to the correct (72) empty spot on the rear fuse block.

When I'm back from Christmas travel, I'll pay dealer to install this harness. Until now I've only pulled my motorcycle trailer which has surge brakes as opposed to electric brakes and I haven't needed a brake controller. Now step-daughter has horse trailer with electric brakes and I'd like to be able to loan her my car on occasion, as her ancient pickup isn't really long highway trip usable.

BTW, the "weak welds" on my hitch were corrected long ago via factory recall or service campaign.