Well, whatever the problem was, it seems to have resolved itself! I connected up the trailer using my new 13 pin plug and cable and everything worked including pin 9 permanently live and pin 10 going live once the ignition is switched on. I’ve connected pin 10 on the trailer to a voltage sensing relay which works as expected, i.e. no voltage output until the engine is running and the alternator is putting out 14+ bolts. So that’s what I’ll use to charge the trailer battery.
I can only assume that without the trailer being attached the trailer module doesn’t send power to pin 10 although in the past I was able to measure 12 volts at pin 10 in the towbar socket. But whatever, it now works.
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Simon J
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