Tow bar electrics

[chrisbrad66]

Hello all i fitted a new Westfalia detachable towbar and 13 pin euro electric harness with bypass relay and split charge relays to my w220 s class a few weeks ago, when i hook the caravan up i get a dashboard message brakelight failure and it switches a reserve brakelight on i.e the reverse light, when i press the brake pedal the brakelights on the caravan flash momentarily then it brings the dash warning up as above, do merc do a specific wiring harness that fits into a plug connector already in the car to make a bypass relay not needed? i feel the car is too clever for its own good with the diy unit, i double checked every connection and can find nowt wrong, all the other lights function correctly. Thanks for reading.

 

[grober]

this any help ? doesn't seem to list the S CLASS? http://www.westfalia-automotive.de/index.php?id=home&L=1

 

[chrisbrad66]

Thats who i bought it off lol, seems they supply a generic harness, one size fits all but not in my case. Thanks

 

[partsspecialist]

will a 13-7 pin adapter not fix this? sorry i dont know much about towbars

 

[BTB 500]

DIY-fitting non-OEM towing electrics to a car as electrically complex as a W220 sounds a bit optimistic IMO.

Presumably it's seeing the extra current drawn by the caravan as an indication of a wiring circuit fault?

 

[chrisbrad66]

my opinion too but the check relay is supposed to fool the system, it does on all the rear lights except the brake lights which on the w220 are LED whereas all the other rear lights are conventional bulbs, i wonder if this is the problem because LED's use less voltage? mmm any help anyone?

 

[BTB 500]

If your towing electrics use relays to drive the caravan lights (rather than them being powered directly by the car's lighting circuits) all should be OK. But I suppose it's possible that the switching side of the relay consumes enough power to confuse a circuit that only powers LEDs normally (much lower current than bulbs).

I would be talking to whoever you got the towing electrics from.

 

[Piff]

Dedicated wiring looms are available as an extra from most suppliers. When I was looking for my ML recently the cost of a dedicated kit varied from £32 to £71