Towbar Wiring

[grumpy13400]

I bought a caravan earlier this year, and had a Westfalia towbar with dedicated 13 pin electrics fitted to my 2009 W211 E280 CDI estate. I also have a small trailer fitted with LED lights.

I have had no trouble with the road lights on the caravan, but today I fitted a 13 to 7 pin adaptor and tried the trailer lighting. As soon as I plugged the trailer into the car, which was not running, some of the LEDs in the rear lights glowed dimly. I started the car, and the rear lights remained the same, but 1 LED in the L/H indicator glowed dimly. The brake lights worked fine, but the indicators, although working, would only flash once every 3-4 seconds although the car indicators worked normally.

Thinking the worst, I first checked the 13/7 pin adaptor, that was fine, then went on to the forums to see if anyone else had a similar problem.

I found a youtube video that showed how to fit a towbar and dedicated electrics to an E class estate, and towards the end of the video after installation was complete, the dialogue said to test the electrics with a test set-up, but Not one with LED lights.

Does this mean I will have to change the trailer lights to ones with normal bulbs?

Has anyone else had a similar problem? I would appreciate any help, advice, comments etc.

 

[Marku]

If it is OK with the caravan it would seem that the trailer is wrong. Use an adapter on the Viano and have used all sorts of trailers without any problem.

 

[Druk]

I had a my2003 211 with factory towbar and electrics. Several anomalies occurred with this during my ownership. It would fail the MOT testers cheapo handheld and some hired trailers wouldn't work with it. My solution was to have my own trailerboard with 13pin plug so that at MOT time or if I needed to hire or borrow a trailer the lights always worked. I have no idea why it should be like this because, like you, the caravan lights worked right out the box however it did make life simple.

Edit... You might be right about the LED's. The rear SAM that controls the lights might not play with them. That would also account for the cheapo handheld tester.




.

 

[dozypillock]

I had a my2003 211 with factory towbar and electrics. Several anomalies occurred with this during my ownership. It would fail the MOT testers cheapo handheld and some hired trailers wouldn't work with it. My solution was to have my own trailerboard with 13pin plug so that at MOT time or if I needed to hire or borrow a trailer the lights always worked. I have no idea why it should be like this because, like you, the caravan lights worked right out the box however it did make life simple.

Edit... You might be right about the LED's. The rear SAM that controls the lights might not play with them. That would also account for the cheapo handheld tester.




.

I did not realize the towbar electrics are part of an MOT test? Is this a new thing?
I should be ok as had mine properly fitted earlier this year, and correctly coded for the car etc, and works ok on my caravan. Not tried it on my trailer, as normally use another car for that, due to not wanting to grease the towball on the merc.

Neil

 

[brucemillar]

I thought you didn't grease modern towballs? It buggers up the friction pads on the tow hitch.

Sent from my iPhone using MBClub UK

 

[dozypillock]

I thought you didn't grease modern towballs? It buggers up the friction pads on the tow hitch.

Sent from my iPhone using MBClub UK

That is correct. Caravan has an Alko hitchlock with built in pressure pads for stabilization so has to be spotless, and grease free.
Trailer is old type hitchlock, so should be greased.

Neil

 

[brucemillar]

That is correct. Caravan has an Alko hitchlock with built in pressure pads for stabilization so has to be spotless, and grease free. Trailer is old type hitchlock, so should be greased. Neil

Just me being a picky sod.

Sent from my iPhone using MBClub UK

 

[BTB 500]

Just to add that the factory towing electrics on my Vito (13 pin socket) don't work with an LED tester, but they are fine with the caravan (which has bulbs in the lights). So it must be something to do with the low current draw with LEDs.

 

[Minz]

When I had my Westfalia towbar and electrics fitted, it stated that it was not compatible with LED lights. At first I thought it meant the LED lights fitted on my facelift C220 estate. It does however refer to the new LED style lights on trailers. Shame really. When I built my trailer I fancied fitting LED style light units but it appears that they are indeed incompatible.

 

[BTB 500]

Yup M-B factory fit is generally Westfalia, certainly the case on my Vito.

 

[Druk]

^ That's what P F Jones told me but I bought an Oris because that's what the S211 had and it has a greater towing limit on the plate than the Westfalia.

Cept it was a crap fit needing the chassis holes reamed out so I wish now I'd just gone for the Westfalia.

The wiring loom was Westfalia however and the sparky that coded the car told me there was a relay missing which he had to supply and fit.

You just can't get the staff................

 

[Minz]

Just as an aside on the greased/ un-greased towball issue. When I had my caravan with an Alko style hitch, I would clean the bulk of the grease off with a rag and then finish off with a good blast of brake cleaner.

Watch out if you have a caravan and are offered the option of having it positioned on a touring pitch by the site owner with his 4X4 or tractor. I've seen quite a few 'helpful campsite owners' siting 'vans with greased or non greased tow hitches with no regard for the cross contamination of friction pads between vans caused by the lack of cleaning between lifts.

 

[Troon]

The bulb failure detection works by pushing a small current through the circuit. This causes the LED with the lowest forward voltage on that circuit to glow.

The solution is to install a suitable resistor in parallel with each LED.

 

[brucemillar]

and... As another aside. When I had my caravan (twin Axle Avondale) I invested in an ALKO Hitch-Lock. Very smug I was too with my new purchase. This until the local plod informed they are useless as Mikey the Pikey uses a tow ball ground down to a spike which fits neatly inside the hitch socket, lock 'n' all.

 

[Minz]

Tell me about it. We had our twin axle Eldis Crusader Sirrocco stolen off a secure storage site by the pikeys with a transit pickup and burning gear. All caught on camera and taken in a total time of 11 minutes. After removing two wheel clamps and a hitchlock with the oxy torch, they then dragged the 'van through a border of mature conifers and off over a ploughed field. B'stards.

 

[davidjpowell]

and... As another aside. When I had my caravan (twin Axle Avondale) I invested in an ALKO Hitch-Lock. Very smug I was too with my new purchase. This until the local plod informed they are useless as Mikey the Pikey uses a tow ball ground down to a spike which fits neatly inside the hitch socket, lock 'n' all.

You can get a 'hard' ball to lock in now. Ultimately if they want it they are going to get given enough time though.

 

[BTB 500]

and... As another aside. When I had my caravan (twin Axle Avondale) I invested in an ALKO Hitch-Lock. Very smug I was too with my new purchase. This until the local plod informed they are useless as Mikey the Pikey uses a tow ball ground down to a spike which fits neatly inside the hitch socket, lock 'n' all.

Al-Ko supply a ball that goes into the socket before you put the lock on:

 

[BTB 500]

Watch out if you have a caravan and are offered the option of having it positioned on a touring pitch by the site owner with his 4X4 or tractor. I've seen quite a few 'helpful campsite owners' siting 'vans with greased or non greased tow hitches with no regard for the cross contamination of friction pads between vans caused by the lack of cleaning between lifts.

Also watch out for roadside checks by the Police. They will un-hitch and check your noseweight using a gauge inserted into the hitch ... you need to make sure that's not contaminated with grease (usually it is).

Also also with most modern towbars you need to strip the black coating off the ball before using it, or it will clog up the friction pads.

 

[BTB 500]

Ultimately if they want it they are going to get given enough time though.

For sure.

Twin axles in particular, when I used to keep my caravan in storage the site was raided two or three times and only twin-axle caravans were taken each time.

 

[grumpy13400]

Update.
Today I decided to make a temporary trailer board using some old trailer lights I had with bulbs in, as opposed to LEDs.

Plugged it in, started the car, and everything worked exactly as it should, which was a relief, as I thought I might have damaged the electronics in some way.

So it seems that if you have an E class towbar with Westfalia dedicated electrics, you CANNOT use LED road lights on your caravan/trailer. They have to be ordinary bulbs.