Brian23
Senior Member
I have a 2005 Eclass Estate and I am looking to fit a towbar. How difficult is it to fit one on the driveway and will the car automatically accept the electrics or do you need other accessories for the electrics?
I don't know about the 211 but I've done a couple of 203's.
On those you remove a rear cross member and the tow bracket goes back in its place. I would look at the kits online and the drawings are likely to show how that might be the case.
Online instructions may even be available.
As for the electrics, my 639 has the oem kit and I see no advantage to having that.
A towing relay like this
Universal 7 way bypass relay electrics TEB7AS Towing electrics Tow Bar Electrics | eBay
isn't difficult to get your head round.
Basically there is often a fuse at the rear that will supply the trailer through the relay and outlet.
The relay picks up the signals from say the indicators and passes the power to the trailer, fed from the fuse.
Advantage here is that a trailer fault will take out the supply fuse and the car is left to function normally.
You can also run a sounder to the front, this will bleep with the indicators as a reminder, I just left mine at the rear.
I fitted a towbar to my w212 saloon on the patio at the back of the house,,,the mechanical part is not difficult, once you have the rear up on axle stands for easy access. For the electrical part, I had the Son-in-Laws help ( he is an IT Techie, and just love's modern car electric's ) He identified a live feed at the back and hooked it up to a by-pass relay, and it's working fine. I have fitted a lot of towbars over the year's on different makes of car's. The last one ( prior to the w212 fitting ) was on a 2014 Skoda Octavia, and for this I used the same type of by-pass relay, only difference was I took a live feed from a fusible link at the battery terminal, and ran it back through the length of the car. worked perfect too.
But as ajlsl600 said....Its much more complicated on modern cars that in the past...electrics were much simpler, you just spliced the cable from the trailer socket directly into the corresponding wire on the rear lamp.
If you do it once, you will not have any problems repeating the process in future.
You can avoid all this if you opt for the Mercedes dedicated towbar wiring harness, which plugs directly into the box, and is connected to the internal wiring canbus.
Good Luck with it..
Hi Brian.. on my W212, in the boot, at the drivers side, when you remove the vertical carpeting, that's where the SAM unit is. I have attached some images to show you how and where it goes. OK? I think that if you use the dedicated MB tobar wiring harness, it's basically just plug it into the SAM unit. If you will use this harness, I think that when you purchase it, the supplier will pre program it for your particular car. For me, the By-pass relay works fine, no pre-programming needed,as I only pull a light trailer. But if you are planning on towing a Caravan etc the MB one is what you need. If you are going to tow a caravan bear in mind that automatic transmission will need additional cooling, in the form of a larger capacity cooling radiator, and possibly change of cooling fan. You will have to check this out yourself, as I have not done it ( yet !!!Hi thank you for the info. When you say that the Mercedes dedicated towbar wiring harness, which plugs directly into the box. Which box do you mean,
Brian
In modern cars, the electric system is called a CANBUS. Basically, ( and very basically at that ) it's a bit like the human nervous system. Everything is linked and communicates with each other via the on board computer. So when you add / subtract in the system, the system has to be programed to recognise the changes. In some cars, something as simple ( formerly ) as replacing a bulb, now mean's programming the system to " accept" the new bulb. For simple towbar electrics, the CanBus is by passed ( with literally ) a bypass relay. This relay is fed electrically without "Disturbing" the CanBus, and all the tail light functions are run via the relay...again letting the CanBus "sleep". So the peace and tranquility is preserved. !!!Having looked into this it seems that:- For those vehicles equipped with a check - control system, it is necessary to use a wiring kit with a bypass relay or a specific wiring kit.
What is this?
Is there an advantage to the 2nd option?
More complications, but not unique to MB, a quick looksee on EBay and Amazon produces Trailer Recognition Control Units for most of the Major Brands.As I understand it, if a towbar is fitted to a Euro 5 or Euro 6 car, unless programmed correctly, the car electrics will drain the caravan battery whilst towing, as the main car battery only charges to around 70%, to allow for regenerative braking.
I could be wrong of cause.
More complications, but not unique to MB, a quick looksee on EBay and Amazon produces Trailer Recognition Control Units for most of the Major Brands.