W210 Towbar fitting

[IanT]

I've searched but this is all I found...

http://mbclub.co.uk/forums/showthread.php?t=7143&highlight=towbar+wiring

OK, I'm going to fit my genuine MB towbar, possibly tomorrow. The electrics question bothers me a little. I reckon I should be able to make my own bypass system either by wiring in FETs or FETs and relays between each bulb connection and the trailer socket.

I have a socket, some wire and will buy FETs if that looks like the way to go.

Looking at it logically, there should be no more than 2A drawn from any pin on the trailer connector, so FETs alone should be sufficient to supply any current required without using relays, plus they won't draw any current from the car loom.

I've had some other ideas too... if the bulb failure system places low voltages onto each bulb to test it without lighting it then I could use some CMOS logic to provide a hard switching level above the voltage that will cause the bulb to begin glowing.

So, am I on the right track, or should I just go out and buy a ready made system off the shelf?

Ian.

 

[robertjary]

Check this link

http://www.rydertowing.co.uk/towbar_relay_technical/towbar_relays_TF1016.htm

As well as giving lots of information, you may find the price of the ready made unit makes it worth considering.

Good luck, Robert

 

[IanT]

Robert, thanks.

That was the site that got me thinking about diy but the prices are reasonable. They pretty much say how they do it on there too, their 'microchip controlled' 7-relay bypass system uses a PIC, probably using its analogue to digital converters to avoid bulb test signals causing the trailer lamps to light.

Ian.

 

[IanT]

Robert,

I thought I'd seen prices for the Ryder kit but now can't find them. Did you have any other info? I've Googled around but still to no avail, plus my local caravan centre hadn't got a clue what I was talking about.

Ian.

 

[robertjary]

Hello Ian,

I phoned Ryder to find a stockist in my area - I ended up with Britannia Towing
http://www.britanniabristol.co.uk/
in Bristol.

Regards, Robert

 

[Benzowner]

Hi Ian,

If you plan to install a 13pin or 2 x 7 pin sockets, check out the current draw on the fridge, its a lot more than 2 amps, and needs its own relay so it only draws current when the engine is running. I've got a detachable tow bar on my W210 estate with a 13 pin connector, bought the car with it on, lucky for me. :bannana:

 

[IanT]

Cheers Robert, I'll do the same. The towbar is now fitted, thanks to some excellent instructions from Dieselman.

I took a couple of pictures and will put them together as a simple How-2, amalgamating them with the instructions.

Geoff, I'm not towing a caravan (yet...) I only intend to tow car trailers so I can move dead cars about legally. The W210 seemed the obvious choice, being able to tow braked trailers of up to about 2,100kg. I've read about the fridge problem though, our family car about 20 years ago didn't have the relay and was push started the only time it died. After that a relay was fitted.

Ian.

 

[Dieselman]

Ian

The Ryder relay is about £25 unless you can get a bit discount.

It should be available anywhere.

Regards

 

[IanT]

I called Ryder and they put me in touch with someone local that has an account with them. Mine has cost £32 and will arrive Friday.

Seeing as the chap doesn't fit towbars any more (no one in the 01689 STD code now) I thought it was pretty decent of him to order it for me so I won't begrudge him the £7.

I've fitted the 7-way socket to the bracket on the beam, routed the cable upwards through the corner of the spare wheel well (most direct route) into the boot. I'll take some photos of that too. Where was the factory position for the cable to come up? I couldn't find anything sensible so I just drilled and reamed my own hole, fitted a grommet and brought the cable in with only about 3" length between the back of the socket and the panel.

Ian.