Interesting comments, thanks. Everything worked fine with my previous trailer which had normal bulbs, and on my small trailer which has bulbs. I thought I'd move to LEDs as they are supposed to give less trouble with blown bulbs and rusty contacts. The Discovery 3 has a bulb check function, so...

Well, resistors didn’t fix the problem. I’ve checked the voltages at the terminal box on the trailer. With everything on the car switched off there is still a small voltage supply at the trailer terminals, on the two indicator terminals it is just under 0.7v, and on the others it is around...

Apparently I need to instal resistors in parallel to the LEDs, ordered, I’ll give it a try.

I’ve just got a new Williams trailer, factory fitted with LED lights. The orange indicator lights flash constantly as soon as the trailer is connected to the car. They flash about 3x faster than normal and about half brightness. The reversing sensor no longer switches off when the new trailer...