Thread: D4 trailer detection

Take a read of the various trailer stickies above.
The reason it’s not detected is your trailers LED indicators do not have to same impedance as a traditional 21W globe which is what the Disco is looking for.
All you need to do is wire a single (or pair - up to you), of ballast resistors in parallel to your indicators of the trailer for the Disco to detect it.
Other ways of achieving this are described in the stickies but that’s it.

LED Load Resistor - Products - Narva

Reinforcing what DiscoJeffster said, I also have a late 2016 D4 and a collection of 5 trailers (don't ask!).
I found that the trailer detection worked for any of the trailers with incandescent globes, but failed for those with LED blinkers.
From ebay i sourced 2 plugs to fit the Disco white and black sockets which I wired to a 12-pin socket, with a 10W resistor (from an auto parts store) in parallel with each of the blinker circuits. The white plug provided additional circuits (eg switched power) that were needed for some trailers, but if those additional circuits are not needed, then just a black-plug to 12-pin adapter is all you would need. This harness works with trailer detection for all my trailers.
Cheap and easy to do.

Thanks guys I will give the load resistors a go. Just purchased 2 and will connect up this weekend.

You only need one load resistor to ensure the trailer detection works but then you won't get the trailer indicator for both sides on the dash when you use the indicators. I have my box trailer done this way, it uses one less resistor and means less work. It is a good idea to have the resistor heatsinked as the can get fairly hot, not a problem day to day but if you stop with hazards on for a while it could cause problems.

Just to reiterate the load resistor has to be parallel to the led indicator.

I use different trailers so I have a load resister wired to each indicator circuit,behind each tail light,with a switch to control the two of them.

Easy to do.

It's been covered in other threads but there is a company in VIC called Linear Electronics Design that make various options for this problem.

Linear Electronic Design | Home

I've got one of their boxes wired into my D4 .... which was harder than it could have been due to the Rear Air taking up so much space. However, it's a brilliant bit of kit with an on/off switch for when you aren't towing or are towing a trailer with non-LEDs.

The guys are super helpful too and are more than happy to pick up the phone and talk you through things. They make boxes that fit to the car or the trailer or attach to the power lead.

Originally Posted by Celtoid

It's been covered in other threads but there is a company in VIC called Linear Electronics Design that make various options for this problem.

Linear Electronic Design | Home

I've got one of their boxes wired into my D4 .... which was harder than it could have been due to the Rear Air taking up so much space. However, it's a brilliant bit of kit with an on/off switch for when you aren't towing or are towing a trailer with non-LEDs.

The guys are super helpful too and are more than happy to pick up the phone and talk you through things. They make boxes that fit to the car or the trailer or attach to the power lead.

Like wise.
Great solution.