Electric Brake Controller Problem

I have a Redarc Tow Pro installed on a 150 Prado. This was done by ARB in Dec 2014. It has worked well up until now. It goes into Limp mode on a random basis. Never whilst actually driving but only on start up WHILST the van is connected. This fault does not occur on every occasion. So it’s a bit of a pain after pulling over for a cuppa and on departure find the lights flashing on the brake controller.

If I start the car WITHOUT the van connected, then plug in the van, the problem does not occur. I have pulled apart both car and van connectors and checked wiring. All connections are clean and tight. Resistance on each contact, across the connected plugs, on a wire to wire basis is 0.1 Ohm.

I have not checked the wiring at the controller itself as is too hard for me to get at it under the dash and I don’t really know enough to try. Nor have I checked the wiring between the trailer plug and the electric brake unit either as it’s covered in bog that Kimberley seem to use everywhere. Covers all sins.

Redarc ( they have been very helpful) suggest that there may be a fault in the controller and to replace it with the latest Tow Pro Elite. Whilst that may be an option that I would be prepared to take it won’t help if the problem is in the the external wiring somewhere.

Your suggestions on a cause of the problem would be welcome. Alternatively a recommendation on a good auto electrician would also be useful.

I am in Perth southern suburbs.

Regards John