Thread: Discovery 4 LED trailer lights

There's a giant thread (33 pages or so) on the Discovery 3 and LED trailer lights at Discovery 3 LED trailer lights

But the D4 is slightly different to the D3 in how it works so perhaps should have it's own thread (I couldn't find an existing one in the search)?


Personally I'm seeking a vehicle mounted solution that would allow me to use any trailer (either conventional or LED lighting) and receive the connection benefits (reverse parking sensors turn off, automatic transmission shift pattern adjustment and dash trailer light indicator).
Even better if it's automatic and doesn't need to be switched on or switched when LED lights are used.


I've come across the Redarc ADVANCED TRAILER LIGHTING INTERFACE product at Advanced Trailer Lighting Interface | REDARC Electronics
Their website is light on information but I've contacted them for further details in hope that it might work.

The first paragraph makes me think it's on the money:

The REDARC Advanced Trailer Lighting Interface module is designed to allow late model vehicles to tow a trailer with either LED lamps or incandescent globes, where the vehicle lighting system has complex detection operations such as late model European vehicles, particularly Audi, Jaguar, VW, BMW and Mercedes.

However, rereading it now, the second paragraph makes me think that with it installed the LED lights will work fine, BUT the vehicle won't sense the trailers there (emphasis added on what leads me to this conclusion):

It senses the vehicle lighting signals without loading the vehicle lighting circuit or control module. The Advanced Trailer Lighting Interface draws the power for the trailer lighting directly from the vehicle battery and switches it to the trailer light circuit based on the input signals received.

I would imagine that the vehicles lighting circuit or control module needs to be loaded up in order for it to know a trailer is fitted and make the changes?


Otherwise there is the offering from Linear Electronic Design at https://www.linearelectronicdesign.c...now.htmlScroll down to Discovery 4/5 and for the Vehicle Plug and Trailer Plug options select "In-Car Mount With Switch".


The only other off the shelf solutions I've found involve fitment of resistors on the individual LED trailers used.

Originally Posted by Dagilmo

I used this information on my 2015 and it works perfectly. Thanks Kelvo!!

The only thing, coming back to the OP, is it's not automatic, it requires a manual switch. I'm no expert and please correct me if I wrong but I'm not sure if you could do a automatic set up. The whole point is the car doesn't 'know' there is a trailer connected due to the low resistance of the LEDs so what would trigger the automation?

If you replace the socket with one with a reed switch on the flap/cover, then you could set it to “auto” by adding another relay to the circuit.

Only issue would be that the resistors would then function when a filament fitted trailer was attached.

Of course you could then over-ride by switching the switch to OFF