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Discussion Starter #1
OK, maybe someone has been down this road and can shed some light on this. Please correct me if any info I state is incorrect; it seem astonishingly difficult to get CORRECT and ACCURATE information on what should be a seemingly easy dealer fit accessory! Some preface: I am wanting to put a trailer hitch on. Simple enough. I am avoiding(for now) the aftermarket stuff especially when it comes to the wiring. I've had nightmares in the past with "universal" trailer wiring/adapters and am hoping to avoid such issues if I can, even if it costs a bit more. This pertains to a 2016 Metris passenger van WITHOUT the factory installed tow package.

So.... here we go!


  1. Metris' ordered for the US have trailer prewiring installed at the factory (even if they don't have the factory tow package hitch when they leave the factory). I believe this is true, but have difficulty confirming this! I believe it was stated in a MB press release from 2015 and dealer confirms this from MB training.
  2. The dealer fitted hitch kit is more than just the tow hitch. That's the easy part and probably no better or worse than the tow hitches available aftermarket. I'm referring to the big chunk of hardware that bolts under the van. BUT IT TAKES A BIT MORE THAN THE BOLT-IN HITCH TO TOW. The hitch CAN be found and that is the easy part; but it is just the hitch alone...
  3. Trailer wiring. Here's where it all gets weird. IF these things come "prewired" than logically there should be some kind of "pigtail" harness to plug into the rear wiring (somewhere) and terminate in (likely) a 4 pin flat plug. Makes sense, no? Parts guys can't seem to find this component! A call to MB Vans left them scratching their heads! This part exists for the G-class and Sprinters, and in Europe for some of their sedans and wagons.
  4. I've seen reference to some kind of "module" that plugs into the rear of the vehicle's harness that does "something" to possibly the Blind Spot Assist system so it doesn't go nuts. I've also found reference that it - or a "program" that is installed - also "activates" or somehow compensates for potential vehicle/trailer sway by doing something with the stability control. Parts guys can't find this module either. MB Vans stumped. References to a dealer fitted OE tow package on the Vito in Europe is the source of this, but I can't find a part number or succinct description. Seems to exist in the field fitable OE towing package for the G-Class & GLK & M Class. This module is shown in a crappy YouTube video that conveniently provides useless part numbers - but it was specific to a Metris - so there is a confirmed sighting of a mystery towing module.
  5. I've found references that to do what I am stating above could take "20 hours of shop time" (several internet references) to which I call B.S. Mercedes can't be any more stupid about towing hardware than any other OE manufacturer and NOWHERE is that asterisk after the towing ability that says in the fine print "when properly equipped" indicating that all towing stuff has to be installed on the vehicle at the time of manufacture.
  6. A reasonable OE field fit-able tow package consisting of the above components (hitch, module, wiring, and some kind of programming) is available for the Sprinter, G-Class & GLK & M Class. Seen it. Dealer's put in a bunch. Not that hard. Internet is full of stuff like "dealer quoted $2,500 to put it in my Metris" but no list of parts or substantive evidence that it truly is that difficult. I suspect the dealer couldn't find a succinct part number/numbers or technical guidance and "high balled" the guestimate.
Sooo... what the heck is really needed to do a field installed OE tow kit??? As much as MB hypes the towing capacity, you'd think they would provide a simplified one-number part package with all the goodies and instructions. Dealers could make some coin installing these in the field. Owners could retrofit.

Now, before I flush out aftermarket alternatives, and I know there are some, I really want to get a handle on the OE arrangement and need some hard data like part numbers, etc. Anybody on the board a tech guy at a dealership?? Anybody got an "in" with MB Vans? This is one of those things that just shouldn't be this hard for a commercial vehicle!
 

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I can appreciate your frustration and agree it shouldn't be so difficult. When we were deciding on which Metris to purchase last year I asked the dealer how much it would cost for them to install a hitch on a vehicle that did not have one. My thinking, a hitch was something that could be negotiated if I picked a Metris without one that otherwise had everything I wanted. I was told their dealership would not install a Metris hitch because of systems and components related to suspension, braking, and stability built into factory hitch vehicle. This dealership knows, sells, and services Mercedes vans in the Seattle area and is not exclusively a luxury car dealer. If it was feasible I believe this dealership could do it but they said they wouldn't. Fortunately the dealership had a good inventory so we ended up with van that has a factory hitch. Unfortunately my experience doesn't help with your situation but perhaps a future Metris buyer might take this into consideration if they plan on towing with the vehicle.
 

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Discussion Starter #3 (Edited)
Thanks for sharing mikit!

I think your experience is typical and reflects a lack of information on the dealers part as to what is necessary to field-fit a hitch. In the "bad old days" a dealer would probably take a truck to U-Haul or something and have them do the deed - cutting into the tail light wiring harness and wire-nutting everything back together. Won't work on a Metris. I believe the Metris uses a "can-bus" or similar electrical control system. What I have been able to confirm, positively, after doing a bit more research is:

1) ALL Metris' are indeed pre-wired for a field installation of a hitch and the associated control module.
2) The module is alternately called something like a Trailer Control Module, Trailer Lighting Module, or Trailer Relay. It is a signal processor that provides powered outputs to the trailer electrics and isolates the Metris so that things like bulb monitoring, LED (or lack of) light combos on trailer/tow vehicle, rear fog light functionality, and combining brake/turn/running lights (on some trailers). There are two plugs in the aft right corner of a Metris (by the jack) this module plugs into, with a separate sub-harness to the trailer hitch area that would actually plug into the trailer.
3) MB really has made it hard for dealers to figure this out. My dealer is pretty good, and they have their parts guys on the case but even they are frustrated.
4) Most of what I have learned has come from Vito sites in Europe and Australia, fitting hitches is pretty routine there BUT they use a different hitch electrical connector arrangement than the U.S. and MAYBE a different trailer tail light arrangement so their stuff may not be fully compatible. However, it does validate that this "Trailer Control Module" is a necessary component and for those markets MB can supply it.
 

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I just put a deposit on a 2016 w/5k miles on it because it has the factory installed trailer hitch. Turns out that it doesn't have the harness. Is that likely to be a problem to have the dealer add? I believe we need a 7 pin connector for our trailer.
 

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But even with factory installed hitch and 7-pin wiring connector, there is no support for electric trailer brakes.
 

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Thank the Good Lord Sweet Baby Jesus that I ordered mine with the factory installed hitch! I've never worried about a new truck having a factory hitch & have added one on later myself because it's usually not a big deal. Too much tech is the biggest problem with the world today. S**t don't need to be that complicated!
 

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Too much tech is the biggest problem with the world today. S**t don't need to be that complicated!
German vehicles are pretty much the worst for solving simple problems with excessive technology. The Metris is right up there on the stupidity scale.
 

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Discussion Starter #8
Thing is... the solution is already done and out there. Problem is, no one can seem to find it!
Geeeze... if you're going to boast about the tow capacity of the vehicle you are making, then make sure you are going to sell the equipment to do it and make it easy to sort!
BTW, there are probably several dozen Metris' in the area that were sold by the dealer. None had the "factory tow package". Don't know if whoever is doing the ordering didn't tick that box or if these things get "allocated" by MB to dealers with the dealers having little say in the matter....
 

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I pretty much stopped reading the OP when it got to, "...Metris passenger van WITHOUT the factory installed tow package."

One just has to look at the tow package 'features' and all it's integration with the vehicle electronics/stability/etc to know that installing OE or aftermarket is a big bag of hurt. When shopping for my Cargo van, I was on the fence about the two option, UNTIL I visited a dealer and saw one with and without side by side. The cut-out bumper, the 'mounts', and the 'trailer stability/load' features...I didn't want to deal with any after sales issues and down-time...especially given the factory cost in the $300 range. My wife was very much against it. We don't have a trailer or need to tow at this moment, but I assured her it was a worth while feature and it did cause some headache finding a 2016 MC in late Oct with one.
 

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I regret that we purchased our 2016 Metris passenger van without a tow hitch, and am looking forward to finding a solution to get a hitch and brake controller installed and wired to tow a small open trailer.

I have easily installed aftermarket hitches and brake controllers below on both Toyota and Honda pickups, but there is no simple or clear solution for the Metris that I have found yet. I checked with a few dealers (southern CA) and no one can give me a straight answer.

One dealer (where we purchased the van) quoted me $1,109 in parts plus $1,700 in installation!! Yes, almost $3K for what the dealer could only describe as including a "hitch . . ., a control unit, 2 separate wiring harnesses, 4 wire connectors, 6 screws, 6 bolts & nuts." An aftermarket (Reese) hitch costs less than $200, so the unexplainable $2,800 premium on the rest seems excessive.
 

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Video of wire harness hook up

I found this video a while back, thought I'd post it here. Still need to find a solution to get a round 7 blade plug for my electric brake trailer before I pull the trigger and install a hitch. If anyone has found a solution for this I sure would appreciate the info.

 

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Thanks for sharing mikit!

I think your experience is typical and reflects a lack of information on the dealers part as to what is necessary to field-fit a hitch. In the "bad old days" a dealer would probably take a truck to U-Haul or something and have them do the deed - cutting into the tail light wiring harness and wire-nutting everything back together. Won't work on a Metris. I believe the Metris uses a "can-bus" or similar electrical control system. What I have been able to confirm, positively, after doing a bit more research is:

1) ALL Metris' are indeed pre-wired for a field installation of a hitch and the associated control module.
2) The module is alternately called something like a Trailer Control Module, Trailer Lighting Module, or Trailer Relay. It is a signal processor that provides powered outputs to the trailer electrics and isolates the Metris so that things like bulb monitoring, LED (or lack of) light combos on trailer/tow vehicle, rear fog light functionality, and combining brake/turn/running lights (on some trailers). There are two plugs in the aft right corner of a Metris (by the jack) this module plugs into, with a separate sub-harness to the trailer hitch area that would actually plug into the trailer.
3) MB really has made it hard for dealers to figure this out. My dealer is pretty good, and they have their parts guys on the case but even they are frustrated.
4) Most of what I have learned has come from Vito sites in Europe and Australia, fitting hitches is pretty routine there BUT they use a different hitch electrical connector arrangement than the U.S. and MAYBE a different trailer tail light arrangement so their stuff may not be fully compatible. However, it does validate that this "Trailer Control Module" is a necessary component and for those markets MB can supply it.
Thing is... the solution is already done and out there. Problem is, no one can seem to find it!
Geeeze... if you're going to boast about the tow capacity of the vehicle you are making, then make sure you are going to sell the equipment to do it and make it easy to sort!
BTW, there are probably several dozen Metris' in the area that were sold by the dealer. None had the "factory tow package". Don't know if whoever is doing the ordering didn't tick that box or if these things get "allocated" by MB to dealers with the dealers having little say in the matter....

I'll try to help where I can. Granted, I'm just a lowly sales manager for the Sprinter and Metris units, but I like to try and learn everything that I can to help not only current customers of ours, but also for people trying to figure these things out like the good people here. That being said, here goes....


Sprinter vans can indeed be retrofitted with trailer hitches and some, not all, come pre-wired. If an aftermarket hitch is installed on a Sprinter, MBUSA will ONLY allow the coding for the ECU flash to update software letting the van know that there is a trailer hitch for the trailer stability program IF it was ordered with the pre-wiring and/or factory hitch installed. If a Sprinter has a hitch and wiring installed, but did not have the pre-wiring already on it from the factory, then MBUSA will not allow a dealer the code to flash to the ECU. It has more to do with liability if something happens regarding the trailer hitch installation and if it was done incorrectly. What we, here at my dealership, have been told (because we asked) is that if there is no bulletin in WIS-NET on how to install/retrofit something to a particular model, then there will be no codes given to flash ECU's. That being said, the Sprinter vans that have a pre-wire should all have the code for trailer hitch already in the ECU...because it has wiring. This is also why when ordering all of my vans for inventory, I try to at least put pre-wire on the build. Being that there are no factory options for a trailer hitch AND rear bumper step, I get the pre-wire with bumper step and then an aftermarket hitch can be installed.




Now, on to the Metris. I had to do some digging for this from one document to another and one web page to another. For vans that have E58 (pre-wire) (standard equipment), but do not have Q24 (trailer hitch), there are some parts that need to be ordered. I haven't dug into one of the Metris I have here on the ground to see what all it already has in it, but I'm willing to bet that I'm correct in my assumptions.


With code E58, MB sells a US receiver trailer coupling (no electrical). Part number is: A 447 310 04 00 MSRP: $359
As for the additional components needed, they are:
A 020 545 40 26 -- Socket -- $54
A 447 540 62 36 -- Electrical Wiring Harness -- $57
A 447 900 41 05 -- Trailer Recognition Control Unit -- $306 (this is the successor/newest part number)
A 447 900 63 04 -- Trailer Recognition Control Unit -- $306 (this is showing as the predecessor part number, which tells me that once this stock is depleted, the one above is replacing)
N 0000 0000 32 76 -- Nut (6 of them needed) -- $2.40/each
N 9101 0501 20 01 -- Hexagon Screw (6 of them needed) -- $5.50/each


WIS-NET document number is AN31.10-S-8080EE Your techs should know what that means and be able to look it up.


Total suggested labor times for everything looks to be just under 4 hours according to our ODUS system. When requesting coding for XENTRY system, it looks like it's still referred to as Vito-Class or V-Class in XENTRY system. That will allow the code to be downloaded and then flashed to the ECU to ensure that trailer recognition control unit functions correctly (disables blind spot assist while trailer wiring connected, etc).


Oh, one other thing to note: when 2017 models were available for ordering, a note was placed on one of the first pages of the ordering guide that stated if a brake controller was planning to be used/installed, that a Parametric Special Module (PSM - option ED5) had to come ordered on the unit. While the Sprinters can have the PSM retrofitted because they come pre-wired for PSM install, the Metris vans do not.


Just from what I'm gathering by looking at everything, it looks like parts will run around $825 before tax, plus 4-5 hours labor time to install.


I hope that all of this answers your questions a little better. I've been a Sprinter/Metris manager now for just over a year and I'm steadily learning more things, as well. If there's anything else I can do to help, please do not hesitate to ask.


One last thing: I don't know why other dealers don't seem to order many with hitches, but I think I have 7 or 8 on the ground right now, 2017 models, with hitches installed already. I find it the be the most cost-effective route and even if not used or needed, getting it upfront sure beats having to pay $1,500-2,000 to have one installed later because you realize you need it.
 

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Discussion Starter #13
Scott! You da man!

Thank you so much for doing the legwork on this. What you found validated the components I believed were necessary. You also found an order code for those who my need to put in electric brakes. Once I get on the other end of this exercise I'll post up a summary of the install and do a video of it for future Metris owners. A couple of quick questions:

1) What plug does the harness terminate with? Can you determine if it terminates in the Euro 7 pin or the U.S. 4 pin flat? I suspect it's going to be the same as any Metris with the factory installed package, but I haven't even been able to SEE one!
2) The WIS-NET document you referred to... Is that "installation instructions" or something and where/how would the tech know or find out what to load into the vehicles ECU? I'm trying to get this as simplified as I can for them, then print out this thread so they have some kind of reference. They haven't done this before...

Again, my thanks!
 

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Scott! You da man!

Thank you so much for doing the legwork on this. What you found validated the components I believed were necessary. You also found an order code for those who my need to put in electric brakes. Once I get on the other end of this exercise I'll post up a summary of the install and do a video of it for future Metris owners. A couple of quick questions:

1) What plug does the harness terminate with? Can you determine if it terminates in the Euro 7 pin or the U.S. 4 pin flat? I suspect it's going to be the same as any Metris with the factory installed package, but I haven't even been able to SEE one!
2) The WIS-NET document you referred to... Is that "installation instructions" or something and where/how would the tech know or find out what to load into the vehicles ECU? I'm trying to get this as simplified as I can for them, then print out this thread so they have some kind of reference. They haven't done this before...

Again, my thanks!


You got it, man. Just trying to help as much as I can.


Regarding the harness termination, I would assume that it will be a 7-pin. All trailer hitches that come with the Mercedes-Benz lineups (passenger vehicles, Sprinter, and Metris) are all 7-pin. Gives you the ability to expand to trailer brakes, if needed. I have several Metris vans on the ground with hitches, so I will try to take some pictures to share here with you guys so you know what it looks like. I don't anticipate the harness terminating to flat 4, but I could be mistaken. I am 99% sure that it'll be 7-pin.


The WIS-NET documents are internal MB installation/troubleshooting/information documents accessible to Mercedes-Benz technicians. Shows all torque specs, amperage/AWG for electrical, installation locations, etc. If a technician at a MB dealership doesn't know what WIS-NET is, then they probably shouldn't be working there. The codes that need to be loaded into the ECU actually have to come from Germany after a request is made by the dealership. It's not like you can just go online and download the coding. Request is sent to engineers in Germany, they look at the VIN and request any additional information, and then send the codes to the dealership if approved. For instance, if an electric sliding step was added to a van that didn't have it before (an OEM step, that is), then a tech would send a request to Germany for a specific code to load into the ECU that would tell the van that a step was installed and allow it to extend when the sliding door was open and retract when closed, while also giving an audible alarm if the door is open and engine is running. This is the main function of the PSM: it's like a centrally located CAN-BUS module that communicates with the main ECU and allows for operational electrical circuits dependent on whether hot all the time, only when key on, only with engine running, etc.
 

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What I find most interesting is that the hitch (OEM from factory) is actually a Westfalia and you can see the part number on there. I searched for THAT part number and it pops up as almost $600. It doesn't say what all it comes with, though. Only says 'trailer bracket.'
 

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Discussion Starter #17
Yeah, Scott, that's been part of the frustration. The part on the hitch is different (0400 vs 0004) to the part number you listed individually in your first post. Would be nice if it came with all the rest of the stuff, but can't confirm if it does or not just short of ordering one and seeing what drops out of the box! That OE hitch does tuck up nicely into the bumper, though the bumper needs to be trimmed (no biggie... the extra ground clearance would be worth it).
 

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Discussion Starter #18
Update time!

The list of parts that Scott provided in post #12 is indeed correct. I'm going to go ahead and do an OE hitch install and I'll follow up here on how it goes. I got such a deal on the van I don't mind spending a few extra bucks on the OE setup. These are indeed trailer ready, though it's a challenge for some dealers to figure out what is needed. Scott nailed it. Print that out and take it to your dealer if you are going to go down this route. They will be most appreciative.

What has become apparent though are a few things that may help the next guy:

1) The Trailer Recognition Control Unit is kind of critical. Since the van uses a "CAN-BUS" system, this thing acts like a separate power supply and relay for the trailer electrics. It also interfaces with the vehicles systems and is necessary for the techs to "load" the trailer "program" into the vehicles computer. This should allow the same functionality as a factory installed setup. I'll document what changes or is added once it's installed and operational but am expecting the neat back-up camera trailer mode; auto disconnect of blind spot monitoring; trailer stability control; and trailer bulb monitoring to be functional.

2) You may not need the OE hitch BUT it does tuck up higher than any of the aftermarket ones. Does require cutting out a notch in the lower part of the rear bumper. No biggie. If you can live with the reduced rear clearance, than you can save a few bucks with an aftermarket hitch.

3) Because of the OE bulb monitoring a trailer with LED lights may freak it out. A known issue with European vehicles used a tow rigs. May need one of these to settle things down. Don't expect the dealer or anyone other than a highly experienced trailer place to even be aware of it. The plug has load resisters in it to simulate incandescent lights and keep the bulb monitors happy. https://www.etrailer.com/Wiring/Tow-Ready/TR20141.html

4) The actual trailer harness goes from the jack storage area to the hitch area via a rubber grommet that is located kind of below and behind the jack. Looks like you may have to pull the pumper cover back slightly to get access, but I'm going to see if I can fish it through from the jack side down to the center of the rear bumper. This looks like the "hardest" part of the install. I'll let you know how that goes.

More in a couple of weeks as this progresses....
 

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3) Because of the OE bulb monitoring a trailer with LED lights may freak it out. A known issue with European vehicles used a tow rigs. May need one of these to settle things down. Don't expect the dealer or anyone other than a highly experienced trailer place to even be aware of it. The plug has load resisters in it to simulate incandescent lights and keep the bulb monitors happy. https://www.etrailer.com/Wiring/Tow-Ready/TR20141.html
the OE metris stuff specifically states that LED trailer lights are supported. The only issue that I have had on my trailer (with full LEDS) is that it will show and error for the right brake every once in a while but will clear once the brake pedal cycles a couple times (maybe brake and blinker). This only happens after the trailer has been hooked up, not randomly while underway.
 

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Discussion Starter #20
Thanks Styles!
I must have missed that in the manual... It would appear that Mercedes superseded the controller part number at some point. People have speculated the newer number indeed does support the LED lights. This discussion is coming from the Sprinter guys who have run into some issues with LED lights on earlier models and well as GL/ML guys (the controller, harness, and plug are the same as the Metris) and do indeed use that adapter thingy I referenced. Guess I'll find out one way or another!
 
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