I just installed a hitch on my Canadian spec W246 B250 4Matic and was wondering if anyone has any insight into the tail light wiring. I have 5 wires going to each rear light assembly. One is ground and one is a Diagnostic wire, leaving me with three wires which I probed with the results shown below. These are the LED tail lights. I'm showing just the left side, but the right has the same result. Point of interest. The tail lights have all red lights, no amber lights. The turn signal is red, and it is also the brake light. I thought I would detail everything here in case someone can help, and then the info will be here for the next person that tries. I'm using a trailer adapter that 'reads' the signal from the light wires and send current to the corresponding circuit. (Tekonsha ZCI)

Grey/black - shows current present when Brake, Turn or Tail are active.
Black/Yellow - shows current present when Tail is active
Yellow/White - shows current present when Brake and Turn are active.

My trailer has shared brake/turn, and separate tail so I wired turn signals to Yellow/White, and it works as expected, flashing as a turn signal and when the brakes are applied.
I wired the trailer tail lights to the Black/Yellow wire and they appear to work, at first. However there are two issues. One is that the trailer tail lights will come on randomly, when the lights on the vehicle are off. If I switch my car lights on and off again, the trailer lights go off for a while, but eventually come back on. The second issue is that the trailer tail light wires come on a few minutes after the car has been turned off. They stay on for about 10 minutes, then go out for a while, then come back on again. They can cycle like this all night.

Anyone have an suggestions? I've seen a few posts on MB, Audi, VW, and Porsche forums with the same issue, but so far no helpful answers.

 

Hi! Sorry I can’t help you with your wiring problem but would like
to ask you what make and model
is the hitch you installed? I have the exact same car and am having a hard time finding a hitch for it… Thanks!

 

I installed a Reese 44777 hitch, made for a GLA250. The mounting holes for the GLA250 steel bumper are the same as the B250. I had to put spacers between the body and the hitch to mount it 3/4 inch farther so it would clear the wheel well area of the body. Draw-tite also makes a hitch for the GLA250. What country are you in?




Stock steel bumper under bodywork




Reese 44777 Hitch for a GLA250.




Plates 3/4" thick, same hole pattern as hitch and OEM bumper mounts





Hitch installed on plates, using longer Grade 8 bolts.

 

Awesome, thank you very much for the info and the pics!
I’m in Canada, Montreal to be precise.

 

I got my hitch at Canadian Tire. The Reese model is 44777. Drawtite model is 75223.

 

Great thanks, I found both models online, but the bolts on the bumper seem welded on from what I can see in online pics, does that mean you didn’t reinstall the stock steel bumper?

 

That is correct. You do not reinstall the stock bumper. The hitch replaces it. The instructions show it being reinstalled, but I suspect that is so that they don't have to provide the hardware. With the OEM Mercedes hitch you discard the OEM steel bumper. I'm not sure but the bolts on the OEM steel bumper may be pressed in, like lug nuts on a domestic or Japanese car. You may be able to get longer ones pressed in.

 

Makes sense,
I didn’t know there was an oem hitch, probably discontinued a while back.
I have the oem roof bars that I can install and would just need to purchase a bike rack but I prefer a hitch rack, just need to figure out what’s less of a hassle/cost…
Thanks for your replies!

 

It was never offered in Canada. There is an OEM hitch and several aftermarket ones available in Europe, but they all use the 50mm fixed ball standard, and not a receiver style hitch. It also comes with the full wiring kit, but then you have to get a dealer to program the trailer adapter, and I doubt a Canadian dealer would be able to do that since it was never an option in North America.

https://etowbars.com/Towbars/Mercedes/Class-B

 

I had seen the euro ones but as you pointed out there’s no receiver only a ball so no go.

i decided to go with a roof rack for now as it’s less hassle than fabricating the spacers and the installation of the hitch bar and I already have the cross bars. I’ll see how it goes and maybe do the installation next year if I’m unhappy with the roof setup. Thanks again for the info!

 

Dear WellKnownHermit,
First I want to thank you for putting an end to many years of doubt I had contemplating getting a hitch for my B250. Your post was great!! Then, if I may, I have the following questions:
-How did you fabricate the 3/4" spacers? Do you have any suggestion on how I should go about doing this? I was thinking of getting a 6mm plate, drilling holes and then sandwiching a slightly oversized nut on each bolt between the plate and the hitch. So it would be: Body of MB ->6mm steel plate->(loose)nut->body of the hitch. Would that work?
-What bolts do I need? You did mention they need to be longer and grade 8 but I'd appreciate it if you remembered those numbers for length and size/thread.
-And lastly, did you ever solve the electrical? If no, I am an electrical Engineer and will have to attack this later... at the end, it is not impossible for me to be of some use to you....
Thank you in advance,

 

When I installed a hitch om my ML350 I wanted to completely isolate the trailer wiring from the vehicle electrical. I used

It uses inductive couplers and takes its power directly from a battery supply. I ran a line to the fuse panel under the right rear seat. The inductive couplers are a tight fit behind the light housings but there's room for them. Not a difficult install by any means.

 

Nice. Thanks. I'll look into it to see if your solution for the electrical also fits my B250

 

Sorry for the delay, I've been travelling. For the spacers I went to an industrial metal supply, found some steel that was the same width as the hitch mount, had them cut me two pieces the length I needed to match the length of the hitch mounting area, then I put the hitch over the plate and marked the holes and had them drill the holes. The plates were $20 and the drilling cost me another $20. Once I got home I painted them with RustOleum primer. I see what you are saying about sandwiching a 6mm plate between two bolts but that doesn't solid to me. I feel that the bolts might bend under load. If all you can get is 6mm plate, then use at least three of them per mount

I don't remember what length I used, but the studs on the OEM bumper piece are M10x25mm. Factor in 5mm for the thickness of the hitch and then another 20mm for the spacer (or whatever thickness you get, but it has to be AT LEAST 3/4" thick to clear) and you are looking at
M8 x 50. Metric is harder to find depending where you are located so you can use Grade 8 bolts, 5/16 diameter and 2" length. The thread doesn't matter as long as you get matching nuts.

Good luck with the electrical. If you have the LED tail lights and get it to work properly let me know.

 

Yup, that's the same one I used. I suspect my issue has to do with the full LED tail lights instead of traditional incandescent bulbs.