Thread: The rear fog lights come on when I plug the trailer in

Thanks Nomad9,

I want to try to keep the wiring on the trailer as standard as I can (just in case I have to tow it with another vehicle), rather than wire it to suit the car. I think it's a job for next weekend!

On my 2008 build D3 the wiring is still wired per the UK standard which uses the brake wire as one of the feeds for the clearance lights. This causes the trailer brakes to come on when the park lights are switched on. I believe some dealers cut the wire feeding the second clearance lamp circuit on vehicle delivery, but mine was not done. Do a search on trailer wiring on here and you may get a few more answers.
The Australian trailer wiring scheme allows for the pin on the trailer that supplies power for reversing lights to also provide 12v auxuillary power so that might be something worth checking.
I'd follow sniegy's advice re pin 2 and check what has been wired up to your float on that wire.
I have pulled many different trailers with my D3 and the only problem I have had is the one where the electric brakes come on with the park lights. I use a standard round to flat adapter plug purchased from an auto accessory shop to tow these.
LED Tailights will complicate the issue further as the Disco 3 sends a pulse through the trailer wiring to test for blown bulbs. This will illuminate LED taillights but not incandescant ones and causes an annoying flash on the blinkers. There are boxes you can buy to fix this but it's easier to use normal taillights if you have the choice ( search for pulse shunt )


IMHO you dont need relays to isolate the trailer wiring although this would probably also fix the flashing problem with the blinkers as the relay would not have time to make contact and illuminate the LED blinkers when the pulse is active.

Regards,
Tote

Originally Posted by Nomad9

Hi DDdisco,
Funny you should mention this, I've installed a Tekonsha Prodigy brake controller in my 2005 D3, I ran the blue wire from the brake controller right back to the trailer wiring connection behind the nearside rear bumper under the light cluster. I wired everything up making sure everything was right, made sure I didn't do the mirror image wiring trick where you wire things up the mirror image that you are supposed to do. I checked the wiring for the trailer, the whole deal.
Despite all this the trailer brakes wouldn't work. I've given up now trying to figure out whats going on, the blue wire behind the bumper comes out as the black wire connection in the trailer plug. For me it was easier to change the wiring on the camper trailer to suit. Everything works fine now all the other wiring worked a treat with no changes. Got me buggered this one, I even wired up a separate long lead to connect the trailer to the vehicle in the shed (a suggestion from someone on this forum), this made things a lot easier than trying to get the camper near enough to the vehicle to try things out.
Wiring things up to the connector at the back behind the bumper bar was the way to go, saves making a mess of the can bus system like I did first time round. It's a pain in the butt running wires the full length of the vehicle but this I've found personally to be the safest way to do this. Hope this helps.

Nomad,
Please say someone has cut the 2nd park light circuit wire!
Find the fuse box in the l/h/r section of the vehicle behind the little panel, (also refer d3 wiring trailer brake instructions)push tab back & remove fuse block toward inside of vehicle.
Cut the brown wire an inch or so away & solder the fuse block end to the black wire next to it.
If you dont & you are towing & you travel through a tunnel at 100kmh & the lights are set to auto the brakes in the trailer you are towing will come & your pants will need to be replaced.
Any queries dont hesitate to ask.

Sniegy,
In all honesty I haven't done this but I will, I did the same mod on my first D3 and didn't have a problem, but I also didn't have auto lights. Muchly appreciated. So the brown wire that is now an inch long gets soldered to the black wire next to it, what happens to the other end of the cut wire? Do I just cap it off and make it safe? Which side of the fuse do I cut the wire, the in coming or the out going wire? Does it matter?

Well, the D3 went off to the local dealer yesterday to get them to look at the wiring and fit the brake unit. They where wholly unhelpful and disinterested, and said to take it to the local 4WD place to get them to do it.

Originally Posted by Nomad9

Sniegy,
In all honesty I haven't done this but I will, I did the same mod on my first D3 and didn't have a problem, but I also didn't have auto lights. Muchly appreciated. So the brown wire that is now an inch long gets soldered to the black wire next to it YES, what happens to the other end of the cut wire? This wire now becomes the connection point for the blue wire from your trailer brake controller Do I just cap it off and make it safe? Which side of the fuse do I cut the wire, the in coming or the out going wire? Does it matter?There is only one side that has these colors

Nomad, sorry for the late reply, been very busy.

Originally Posted by DDdisco

Well, the D3 went off to the local dealer yesterday to get them to look at the wiring and fit the brake unit. They where wholly unhelpful and disinterested, and said to take it to the local 4WD place to get them to do it.

. If u need some help doing this ring me 0414 533 085 HTH

Just an update. Had the Hayman Reese brake controller fitted, and it works perfectly, except the rear fog lights are still on whenever the trailer is plugged in.

I disconnected the trailer pin 2 wire (still haven't had time to see what it is connected to), and it fixed the problem.

Thanks for all your help.

Originally Posted by sniegy

Can i ask who wired in the trailer brakes? if you have them, Was it a dealer? or a recommended auto electrician?
You need to be careful who wires in the trailer brakes as the wiring needs to be modified not to cause problems.

Hi Pete,

I have a similar problem here as I just purchased a camper trailer (not LED lights) and went to plug in the trailer and the rear brake lights on the D3 come on. No ignition on. When you mention wiring, who should I take the car/trailer to? Will any auto electrician do, or does it need to be someone who knows Land Rovers? I usually use ULR for all my servicing, but if you can recommend anyone, I'd prefer someone that knows what to look for. Problem is I don't wan tot tow it plugged in or without lights....any idea's. I could try testing the plug, but I'm no electrician.

Cheers Neil.