Never had any issues towing with a few RR until now.
Last trip all lights on caravan working except side lights (f&r) and numberplate. All other lights and fridge ok.
Tested the car with a Sealy tester and all lights including side lights ok - albeit this is no load.
The RR was serviced the week before the trip, may be a red herring.
My problem is that all lights on the van use a common earth, so if the van earth had an issue I would expect all lights to fail.
I know the RR software will pick up some issues, but what possibilities are there to look at.
The RR recognises it has a trailer fitted, and goes through bulb check ok, but I never have a lot of faith in that routine.
Any advice and pointers would be appreciated. 2008 Vogue Black - gone
2012 Vogue SE White - gone
2016 Autobiography Blue - gone
2019 Autobiography Grey - gone
2020 SVAutobiography Red

Just to update on this.
Several visits to the Main Dealer proved that the car was delivering 12v to the towing socket pins until the caravan was plugged in when it shut off to the l and r side lights.
Dealer could make it work on a trailer board with single lights, but my caravan had hi and li side lights plus side marker lights all filament bulbs drawing around 3.3 amps.
So the problem was definitely the car sensing too much current being drawn and shutting down the circuits.
So finally replaced stop/tail lights on both sides with LED bulbs and solved the problem.
Replacing one at a time showed at what point the current dropped below the threshold.
Also interesting that it senses both sides together not each individually.
So after a few frustrating months I can tow in the dark.
As my van is all filament bulbs, may replace the rest with LEDs - when it gets warmer!! 2008 Vogue Black - gone
2012 Vogue SE White - gone
2016 Autobiography Blue - gone
2019 Autobiography Grey - gone
2020 SVAutobiography Red