Thread: MY13 Discovery 4 Electric Trailer Brake Wiring

Originally Posted by DiscoDavey

When the manual over ride button is pressed the trailer bake light come on. When the car brakes are applied, the same brake lights come on!

What are you expecting? This seems correct although it doesn't explain why the trailer brakes don't work.

The P3 has a diagnostic mode that can be quite helpful. See link below for what you get when its working. It allows read out of current and voltage just by pressing a few buttons on the P3. The lights you are getting seem OK to me.


http://www.aulro.com/afvb/d3-d4-rrs/...ml#post1419157

Regards
Gerry

Originally Posted by Graeme

What are you expecting? This seems correct although it doesn't explain why the trailer brakes don't work.

When the trailer over-ride switch is activated on the Electric Brake Control, the brakes should activate and I would have thought the brake light on the trailer would not? However, maybe the EBC also sends a stop light signal to the trailer regardless if a foot is on the brake when over-ride activated- that would be why there is a stop light cable running to the brake pin! Would make sense.

Putting a voltage meter on the pin shows only brake light pin working.

I ran the diagnostics and it all looks OK although I am not sure what output readings I should be getting.

I'm going to assume I have a bad connection on the blue cable. I'll re-connect and report back.

If you are just checking the pins at the rear of the Disco, then the readings will not be correct.
You need to have as we do a dummy board with loads & you then get correct readings.
(Have been caught before)
It all looks correct.
If you apply the manual lever then yes you will get a brakes to operate at the trailer, you don't use the EBC unless the trailer is connected.

Cheers

Hi All,
I am new to this forum and have now had my MY13 D4 for just over a month and have been following all threads on trailer wiring with interest. I am a convert from Toyota (4 x Prados) and I have found the descriptions and hints very helpful. I finally got to wire my P3 brake controller in over the easter break and all worked fine initially.
It seem now though that the trailer brake lights do not operate nor the brake controller as there is 0 volts on the 'red' feed wire from the front.
I have wired the controller red wire to the trailer red wire with a diode connecting to the red feed wire. This is so that when the manual overide lever is activated on the controller - the brake lights on the trailer (van) will operate but not feed back to the vehicle.
I have read that others have had similar issues which appear to fix themselves. Can anyone please advise where I should go next or possible causes as at this point I have no trailer brake lights? I have been unable to find any fuses that may possibly be the cause.
Cheers
Keith

Is the diode in the correct way?

The Kathode end needs to face the brake controller not the rear of the vehicle.
Did you connect the red wire from the ETB unit to the red wire at the rear of the vehicle?
(Also be careful a there are 2 wires, it is the smaller one)

Let us know.

Cheers

Sent from my iPad using Forum Runner

Thanks Pete for the quick reply.
Yes the diode is correct - I have 0volts at the anode when brake applied so issue is nothing from the front of vehicle.
Manual overide works fine.
As I said it worked fine to start and I have LED lights and shunt resistors installed on indicators. All other lights work ok and trailer seen as reversing sensors disabled etc.
Cheers
Keith

Hi Pete,
I have attached a photo of the connections and as can be seen from clear heatshrink the diode is correct.