Trailer wiring
Hi. just recently purchased a 2017 GLS450 that has a factory hitch installed. or at least I think it is factory. What is missing however is the trailer wiring. There is no connector for the trailer wiring. Does anyone have experience with installing a wiring kit? Thanks for your help.
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Originally Posted by jpmoylan
(Post 7738492)
Hi. just recently purchased a 2017 GLS450 that has a factory hitch installed. or at least I think it is factory. What is missing however is the trailer wiring. There is no connector for the trailer wiring. Does anyone have experience with installing a wiring kit? Thanks for your help.
They told me the interior has to be rmoved to completely wire back from the dash to the hitch. That is MB does not prewire for the hitch like Ford, GM do. I said forget it. Lee |
Originally Posted by jpmoylan
(Post 7738492)
Hi. just recently purchased a 2017 GLS450 that has a factory hitch installed. or at least I think it is factory. What is missing however is the trailer wiring. There is no connector for the trailer wiring. Does anyone have experience with installing a wiring kit? Thanks for your help.
Originally Posted by BLM2
(Post 7739024)
I do not know how true the following is. I went to my MB dealer last week to get a trailer hitch attached, so I could tow a trailer home with my daughter's apartment posessions. I have a 2018 GLS 550. They quoted me $5,000.00.
They told me the interior has to be rmoved to completely wire back from the dash to the hitch. That is MB does not prewire for the hitch like Ford, GM do. I said forget it. Lee |
1st - if you are in the US - basic trailer wiring can be installed with U-Haul for under $100 which gives you lights and brakes which uses a small relay box (normally Modulite) and splices into rear wiring.
2nd - the "factory" trailer hitch wiring which connects to the full car system is much more extensive - and can take up to 8hrs (or more) of shop time at the dealership. For normal towing the clip-in wiring is fine - for heavy towing you can add a Wireless Brake Controller. Mercedes has extensive features that are connected with the factory installed hitch system - to retrofit/add those connections is a real pain - there is a MB "harness" but the techs need NetStar access to see the wire diagrams - but still like 8hrs+ shop time. |
Hi all, I found this thread useful so I thought I’d update it with some further info.
For those that are towing a trailer / caravan with LED lights, ours cars can’t detect it is connected because of the low power draw from the LED’s. The solution is to wire in some resistors to simulate the power draw of normal incandescent bulbs. I made up two harnesses, one with 5w 33ohm resistors and another with 50w, 6ohm resistors. I made up two because we have different wiring configurations here in oz and I can’t be bothered changing the terminals around - plus I wanted to try the different resistor values. Will try it out and update the results here. The 50w 6ohm will definetly work (but will get hot). I’m not so sure about the 5w https://cimg1.ibsrv.net/gimg/www.mbw...9ae6e5789.jpeg |
Originally Posted by jpmoylan
(Post 7738492)
Hi. just recently purchased a 2017 GLS450 that has a factory hitch installed. or at least I think it is factory. What is missing however is the trailer wiring. There is no connector for the trailer wiring. Does anyone have experience with installing a wiring kit? Thanks for your help.
if “tow hitch” isn’t listed in factory options you have an aftermarket hitch. Go to uhaul and they will install the 7 pin plug which solely connects tail lights. Then order Curt Echo 51180. This is a bluetooth wireless brake controller that plugs into your new 7 pin port. Works great. Caveat: as opposed to factory option, the MB will not know it has a trailer attached. Getting the factory tow option installed after the fact is prohibitively expensive. 10-16 hrs of MB Dealer hourly labor and the entire interior is uninstalled to run the wired connection. Curt wireless essentially does the same thing absent tearing your vehicle apart. |
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