help with faulty hitch electrics

[piggy]

Hi,

I have a 2005 x5 Dsport. I have just paid a profeesional to fit a new hitch and electrics, and he is telling me I have a fault on the car electrics.

When the trailer is plugged in, one of the sidelights does not come on (passenger side). He has traced the cables back to the aftermarket electronics module that comes with the hitch and plugs into the car loom, and he is telling me there is ne signal coming into that box for the side lights.

My question is, would a bmw plug in diagnostic find the problem or not? Since having the wire loom fitted I have got some random messages like "check numberplate bulb" and "check sidelight bulb" that seem to appear once and then not return.

Question 2, if someone has a hitch wiring system that works, do you get any indication on the dashboard that the trailer is plugged in?

Any suggestions of how best to approach this problem from DIY diagnostics?

[XEX05]

I have had a tow hitch fitted to my 2002 4.4i about 10 months ago. I don't have a dash indication light stating when the trailer is hooked up.
When they fitted mine, they left the rear parking sensors disconnected and then tried to say that they always do this as the sensors will constantly go on whilst towing. I told them that I can cancel the sensors manually so would appreciate the sensors be reconnected as I only tow about 10% of the time.
They came back out reconnected them. Apart from that, all other electrics work fine (touch wood).

[Laurence]

Also, when the trailer electrics are plugged in, it disables the rear parking sensors.

[JCL]

Originally Posted by piggy

Any suggestions of how best to approach this problem from DIY diagnostics?

Some aftermarket wiring solutions have worked fine for members here, others have had multiple problems with warning messages and faults similar in nature to what you are experiencing. The BMW lighting system is multiplexed, and uses the same wires that carry current to the bulbs to monitor for imbalanced loads (such as failed bulbs). You may be able to track it down using a wiring diagram. First step would be to disconnect all of the aftermarket wiring and establish a baseline, ie does the vehicle wiring function correctly without the trailer modifications. If not, the modifications may have damaged a lighting control module. If it does work fine without your trailer wiring modifications, then I would simply leave off the aftermarket wiring, and install the original BMW wiring module for trailers. It worked very well for me when I used it.

It does not provide an indication on the dash that the trailer is plugged in, but neither does it send fault codes.