Trailer Wiring Harness for 2004 BMW X3 for a Trailer with Separate Amber Turn Signals

Question:

do you market a unit that isolates the trailer from the car wiring but still retains a normal 5 wire configuration of Tail light Brake light left indicator right indicator Earth return

asked by: Tony

Expert Reply:

I do have a way that you can have separate turn signals and brake lights for a trailer that is set up for it but not a wiring harness by itself that does it. In the US the norm for trailers is actually combined brake lights and turn signals. So what we would have to do is choose a wiring harness for the vehicle, such as # 119250KIT for your 2004 BMW X3. Then on the trailer side, assuming it has a connector that does not mate up with the US 4-Way flat, use a trailer side 4-Way, such as # HM48110.

Before connecting the new 4-Way to the wiring on the trailer you would have to run it first to a special converter, # C56196, which separates out the combined turn signal/brake light circuits. On the input side the green wire will go to the green wire from the 4-Way. Yellow goes to yellow, and white is the ground (Earth). On the output side yellow will be left turn signal only, green is right turn signal only, and red is brake lights. The brown tail light wire will bypass this converter.

Normally I would say to just use a matching vehicle side connector and wire it into the tail lights on the vehicle. But in this case your Bimmer uses a multiplex wiring system with combined circuits so it requires a wiring harness that can handle that sort of complex wiring system which is why the additional equipment is necessary.

expert reply by: Michael H