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 is attached and the trailer turn indicator on the dash no longer works.
The trailer lights work otherwise work normally.
Car has 13pin connection.
Towing car is a Discovery TDV6S, 55 plate.
I’ve seen a few references to this happening, but no explanation or cure.
Any ideas?

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

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 0.25-0.3v. They all pulse.
So what is going on here?
Come on all you electronics geniuses, why is this happening and how do I stop it???

Fastal said:

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 0.25-0.3v. They all pulse.
So what is going on here?
Come on all you electronics geniuses, why is this happening and how do I stop it???

Click to expand...

If the car has “bulb check” features built in, then that explains the voltage and pulsing when the ignition is off (this system check is usually performed constantly).

As for the trailer lights, I know some vehicles don’t like trailers with LEDs in them. My defender doesn’t, and it has LEDs fitted to all current lights (apart from headlights) and the correct indicator relay. It’s ok with the caravan on which uses normal lights, and the few trailers I now use, which also use normal incandescent bulbs. I used to use a trailer with LEDs and it wouldn’t indicate properly.

If you have a spare bulb and some wire, make up a test lamp and try that in the trailer socket. If it works properly, then the vehicle doesn’t like the trailer light setup, if it doesn’t work properly and you have the same issue, then I would guess it’s wired up wrong and needs one of them canbus correction boxes installing.

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 that explains the pulses, I guess.
I've asked for advice from Ifor Williams as it was their agent who proposed the LED's in the first place.
Waiting for a reply.......