Towbar wiring on E46 Facelift Wagon

[E30 325i Rag-Top 2959]

Came across a new one today after wiring in the plug for the trailer on the E46 wagon. I think all the information, and the wiring I got with the towbar, were for a pre-facelift while the car is actually facelifted with the different lights.

The trailer lights are powered off a set of four relays with the trigger signal coming from the cables for the lights on the back of the car, the 12v supply coming from a fused connection on the battery. All work fine apart from the rear (tail or park?) lights which only flicker and the relay is constantly clicking. At first I thought it was a dodgy relay, swapped the wires onto another and got the same result.

It turns out the rear brake and tail light design is a new one on me - whilst there are two bulbs, both come on dim for the tails and then one lights up brighter for the brake, however it is still only a single element bulb. This is done by only a low voltage (3.3v) being supplied for the tail, and then the full 12v for the brake. Which I think is doing two things - 1) the low tail light voltage is not enough to keep the relay open - hence the constant clicking - can I replace this with a lower trigger voltage relay and still swith the 12v? 2) when the tail is on this also raises the voltage of the brake signal wire to 3.3v due to the shared bulb - can this be solved by fitting a diode to stop the cross over?

Any thoughts most welcome.

[antil33t 90]

You could possibly put a suitably sized resistor onto the brake light side, so that the relay doesn't get enough voltage to trigger the brakes, till 12v goes through it.

[*Glenn* 854]

Jochen or Grant might be able to help with this one. You might end up having to get the correct wiring/control unit from the dealer though.

[camera doctor 25]

You could try a solid state relay which is more likely to action with the lower voltage.

For example Jaycar

Or run a wire all the way to the front park bulb ?

Edited January 6, 2011 by camera doctor

[hotwire 352]

Jon - aware of the system but funnily enough - have never thought of nor needed to cross this bridge

If using the unit Greg has suggested - still would require splitting the circuits between stop & tail.

Thinking as I am writing though - this could be done by using an extra changeover relay - with the 3.3v tail supply to the above electronic relay going through the normally closed contacts whereby when brake is on - turns this relay on to open the supply to the electronic unit.

You would also probably need to load the brake relay to stop it trying to activate with tail lights on

[jochen 4]

Just make it simple and fit the proper trailer lamp control module.

Look on ebay

[hotwire 352]

^^^^^ Yep or that. Meant to add that also

[kiwi535 538]

^^^^^ Yep or that. Meant to add that also

and try to stick to a 1 7/8 tow ball(if you want to hire normal trailers) mutter mutter