My Allroad 2004 4.2 Headlight Malfunction Light (see pic) goes on intermittently with a small trailer hooked up to the 13-pin to 4 pin eurohitch adaptor... is there any way to turn this off or fix something I did wrong?

I wouldn't mind but everytime it comes on, it has a very loud piercing BEEEEEP which is driving me crazy!

Also as soon as you put the car in reverse the sensors just stay on... did this add on get wired improperly?

 

That's not actually the headlamp malfunction indicator, it's a bulb out warning but I'm just picking nits.

The system goes by resistance to determine lighting fault. There should be a certain ohm reading through the lighting circuits. If the electrical control module senses too much or too little resistance, it'll command the cluster to turn on the warning.

The trailer lights need to have their own power feed to a converter box. The converter box (basically a small module) uses the hookup to the taillight wires as a signal only but draws no current from that circuit. This way, the resistance is unchanged and the warning will not come on.

Sounds like you have add on trailer lights(?) Check to make sure there is the correct converter box and that it's powered from a battery source. Normally, the wire (about AWG 10 or 12 gauge/ 6.0 or 4.0 mm2 metric) runs all the way to the battery or the battery junction panel.

Sorry, it's kind of hard to explain this in a text format but hope you get what I'm trying to say!

Here is the U.S. we don't have 13 pin connectors. Only 4, 6, and 7 pin so there may be more to it than I'm aware of.