S210 2002 towbar electrics

[Llewelyn]

OK, so these modern canbus etc. cars. I have a universal bypass relay TEB7AS, can I just wire that to the rear lamp feeds in the normal manner? I'm led to believe that this is required (the relay) due to it upsetting the car otherwise and leading to errors if it's driving 2 bulbs where there should only be one. I assume the load of the relay is small enough not to register.

Also any hints and tips on best place to pick up the wiring so as not to run wires all over the place. There are lights in the tailgate and on the rear corners...

 

[Llewelyn]

got a bit closer. The rear/brake etc lamps are all separate filament and supplied by a wire each, so just need to connect into them with the clever relay. Can't see a plug to connect trailer wiring though which would've made life a whole lot easier...

 

[Llewelyn]

In case anyone else is doing this, here are the wiring locations and colours. Get an isolating relay such as the TEB7AS which is commonly available. The relay goes behind the spare wheel on the left side of the car.

In the right side of the car, connect a 2-core flex to grey/red (rear lamp) and black/green (turn signal) wires of the feed to the RHS rear light unit. I ran it under the stainless cover on the back silll.
In the left side, connect those wires to the correct relay input wires. Still on the left side, connect left rear lamp to grey/black, left turn signal to black/white and stop lamp to black/red in the feed to the LHS rear light. In the fat bit of loom that runs up towards the roof, find the grey/green and connect fog lamp input to that.

Bring the wire from the trailer socket along behind the bumper and in through a handy grommet in the bottom of the spare wheel area. Connect the wires to the relay unit, pair up the white wires (earth) from the socket and from the relay and connect to the earth point nearby. Lastly, connect into the feed for the 12V socket in the boot area, and run a 12V supply to the relay.