Well, I pulled the wiring last night - all good now - no issue with CC when the trailer is hooked up.

What I thought was a fused relay turned out to be just two 30A fuses - no relay. One feeding +12v directly from the battery to pin 2 on X393S and one feeding +12v to pin 5 on X393S but via a loop to somewhere up the front of the car, along with a wire tap from pin 6 on X393S. I have yet to determine what this part of the circuit is (was) doing, so I have yet to remove all the door sill trims and covers under the drivers foot well to determine what these wires are connected too. I think there may have been (still might be) a hidden switch up front somewhere and this circuit was to run aux .work lights or something. But I'm just guessing now!! :-)

I had to put two diodes in the trailer connector to tie the tail light circuit to the reverse lamp circuits - our trailers rarely have reverse lamps fitted and the CC expects to see them. Easy work around that seems to work well.

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Wayne
2005 BMW X5 3.0d (b 02/05)
2001 BMW F650GS Dakar (b 06/01)