yes I still require a response to the original question
just to clear things up......
so if the problem is with the towing electrics even when removed this fault would still be logged in the BCMii even though there is no blown fuse or bulbs on the towing vehicle.
The BCMii now logs the fault and doesn't reset once the offending item removed it needs a diagnostic computer to reset, seems very clever to pick fault up but very dumb in that it doesn't reset once the problem has been removed
hope I've interpreted your reply correctly