It was a struggle to find the end of the factory supplied trailer brake controller wiring on my 2017 GLS. It was even more difficult to find good information on the internet and impossible to get information from my dealer!
There is a 4 wire bundle: Larger red/white stripe and yellow/red stripe and smaller black/white stripe and brown. They are intermittently wrapped in a black cloth wrapper. There was a piece of white masking tape holding them up above the carpet.
The wire enters along the left side of the foot well and takes a path up to the top edge of the carpet and arches over to an attachment snap behind and to the right of the brake pedal assembly on the firewall. It then dives down very far under the carpet toward the gas pedal. This was much more difficult than it needed to be which is frustrating.
I was finally able to find the end by removing the trim that goes on the door sill and up to the rear of the foot well. It simply snaps off. This allowed me to pull up just enough on the carpet to free the end of the connector. This was not easy. Not being certain that the connector was there, I was afraid to pull too hard on the wire.
The path of the wire approximately follows the dashed red line on the attached document, but this is from older models.
Succesful Tekonsha Primus IQ Install in Mercedes Benz GLS
The Tekonsha Primus IQ controller was successfully installed in the GLS and we had a great overnight to Tettegouche State Park.
I could not find mention of how to connect brake controllers to the GLS in the manual, or anywhere else in any Mercedes information. The service manager had NO information, not even a Star bulletin when I inquired, which is why I am posting this. Hopefully others will find this helpful.
I used quick connectors that slip over one wire (on the car pigtail) and allow for insertion of the wire from the controller harness (see attached image for reference). For some reason, there is not an adapter pigtail connector available from Teknosha for Mercedes.
Mercedes offers the plug shell and pins to enable quick connection if you want to go that way. You have to purchase the individual parts and connect them to the bare wire pigrtail supplied with the controller.
For the Primus IQ, in the 2017 GLS the wires mapped like this:
GLS Purpose Controller
Red 12 V Power Black
Brown Ground White
Black/Red Light Circuit Red
Yellow/Red Actuate Trailer Blue
Brakes
You should carefully verify your set up for your vehicle and controller prior to wiring, please!
GLS 450, Gas, Twin Turbo V6. Tows '68 Overlander like a dream. Overlander is listed at 4100#. 4 kids, dog, 2 adults. Airmatic Suspension is awesome. GLS has anti-sway technology built in to the traction control computer.
1952 15' Cruisette
1967 20' Globetrotter
2010 19' International
La Cañada Flintridge
, California
Join Date: Jul 2012
Posts: 109
Quote:
Originally Posted by Tbeck11931
Why are you giving up? We found a great 2014 GLS 350 BlueTec for 32K
Because that is what I had that was just bought back by MBZ under the California lemon law. Since they don't sell any in CA as CPO, I am not willing to take the chance of another troublesome vehicle.
1952 15' Cruisette
1967 20' Globetrotter
2010 19' International
La Cañada Flintridge
, California
Join Date: Jul 2012
Posts: 109
I loved my 2014 GL350 BlueTec except for the unexplained problems that had it in the shop for a week every 2-3 months. I wasn't happy to return the car to MBZ and had hoped they would fix it but never could. Happy to have gotten a full refund. I had so many problems, I am really gun shy with this TV
1990 34' Limited
2013 27' FB International
Conroe
, Texas
Join Date: Jul 2012
Posts: 208
Quote:
Originally Posted by kellykellyi
I loved my 2014 GL350 BlueTec except for the unexplained problems that had it in the shop for a week every 2-3 months. I wasn't happy to return the car to MBZ and had hoped they would fix it but never could. Happy to have gotten a full refund. I had so many problems, I am really gun shy with this TV
Sorry to hear that. We have had great luck with ours, glad MBZ to care of you.
I recently encountered the same 'no information from the dealer' issue when inquiring about an EBC on my 2017 GLS550. Finally found a rep at the local dealer who confirmed that Mercedes doesn't install one with the factory tow package. He wasn't aware it was prewired however. Strange MB doesn't offer one...perhaps for liability reasons?
Thank you Bunkroom for solving the issue!!!
I was able to easily find the wiring harness as described, underneath the driver floor mat. The wire colors were nearly the same. I ordered the Tekonsha 90160 Primus IQ Electronic Brake Control off Amazon and installed it literally in minutes.
Just got back from a trip to Montana and the brakes worked beautifully.
2017 19' International
2018 25' Flying Cloud
Monrovia
, California
Join Date: Jan 2017
Posts: 96
While we are on the subject of MBGL class as tow vehicles, I am looking at the GL 4matic to tow a 19' International. For reference, the 19' has a higher tongue weight than the dual axel 23' FB. From the MB owners manual I find the tongue weight listed as 600# on the GL 4Matic. This a relatively light tongue weight rating (<10%) as compared to the max trailer weight rating. Does any one have a tow rating for MB that acknowledges weight distribution? GM is one manufacturer that does list these ratings separate in their owners manuals, the Tahoe is rated for a max trailer weight of 8400#, but the tongue weight is 600#weight carrying, and 1000# weight distribution. Is any one else a frustrated as I am about getting the tow and weight ratings from the vehicle manufacturers?
While we are on the subject of MBGL class as tow vehicles, I am looking at the GL 4matic to tow a 19' International. For reference, the 19' has a higher tongue weight than the dual axel 23' FB. From the MB owners manual I find the tongue weight listed as 600# on the GL 4Matic. This a relatively light tongue weight rating (<10%) as compared to the max trailer weight rating. Does any one have a tow rating for MB that acknowledges weight distribution? GM is one manufacturer that does list these ratings separate in their owners manuals, the Tahoe is rated for a max trailer weight of 8400#, but the tongue weight is 600#weight carrying, and 1000# weight distribution. Is any one else a frustrated as I am about getting the tow and weight ratings from the vehicle manufacturers?
I have not found any tow ratings for MB that accounts for weight distribution hitches. My local Airstream dealer (Covington WA) did not have a concern about the 660lbs tongue rating of my GLS. They agreed that the MB spec seemed very low, and they take into account total tow capacity, trailer weight and the distribution of the hitch instead.
Our 2017 GLS550 tows our 27FB beautifully. There is way more power than I use and remind myself to take the passes at 60mph instead of what the MB wants to do - much faster. I have been checking the hitch and bolt points regularly to make sure no visible stress points are seen. In my opinion the MB is more than capable and the larger V8 in the 550 works beautifully.
I don't see that you revealed the outcome of all your hard work_ Did you get a controller to work? if so which did you go with? We are setting up ( hopefully) a 2013 GL350 to tow a 67 Safari and need controller advice
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