Trailer wiring/Bulb failure/relay unit fault

[mercw126man]

Hello, any wiring experts out there?

I've wired up my trailer socket, and the bulb failure warning light now comes on when the sidelights are on, with the trailerboard connected. The lights were wired in parallel with the car (as is standard practice) terminated at the light unit.

Any ideas of how to stop this, without running extra wires to the feed side of the relay unit (wherever that is)? Incidentely, I used the wiring loom earth (brown wire in the N/S loom) as the earth connection for the trailer connections, for convenience. Would using a seperate body earth cure the fault? I've tried two different trailerboards but they both produce the same fault.

I could just live with it, as I don't plan to use it much in the dark anyway with a trailer, but I'd just like to do the whole job properly, rather than half a job!!

 

[television]

For the lamp out light to be on and no trailer joined up, you must have a lamp out somewhere, even a number plate lamp will do it, if the lamp only comes on after you push the brake pedal, its a stop lamp bulb out.

Malcolm

 

[mercw126man]

Trailer wiring - who needs it!!!

Thanks Malcolm.

The light only comes on with a trailerboard connected, so it is the extra load from the trailer wiring/lights that's being sensed and displayed. What I'm not sure about is whether this is normal on this model, or whether I need a bypass relay (lots of work fitting 'cos I'll have to run a live feed from the front of the car).

I've fitted loads of towbars to cars with bulb failure sensing, and never had to fit a relay yet. Several websites show that the relay is not needed on this car, so I was a little surprised when the light came on.

What do you think? Is it relay time?

(As an aside, I'd thought about fitting LED bulbs to the trailerboard to reduce the load/resistance - would have to be fitted to the trailerboard as I suspect a fault would be shown if installed on the car, due to the minimal resistance they offer, but they're much easier to fit than the relay).

 

[television]

If you wire the way you have (standard) then the lamp out will light, MB had their own special way of wiring to stop this. why worry for the amount of time you will be driving with it. LED's may not help,too hard to say and a relay means a lot more work.

Malcolm