Thread: D4 Electric Trailer Brake Wiring

I can't say for sure on the diode from the picture as I can't really remember the loom that well any more, but to me it looks like you've put the diode after the splice. It needs to be before the splice, therefore is between the Central Junction Box and the splice, not between the splice and trailer loom pickup.

Regarding the brown - blue wire connection, it doesn't seem to be done correctly from your image. I've marked up the pic, if the feed is the black and red pair then your black (blue from EBC) cable need to connect to the cut off brown cable.

So I cut the brown wire and the lights no longer trigger the trailer brakes. The issue I am now having is that the towpro doesn't seem to recognise the trailer. No lights come on the dial and when I try switch to manual nothing happens. Could this be because of the positioning of the diode?

The other thing is that the reverse sensors still come on and beep picking up the trailer. It is like the vehicle has no idea there is a trailer connected.

The D4 recognizing the trailer is independent of the the Tow Pro seeing it.

I'm assuming that your trailer has LED lights... so you need the load resistor(s) or incandescent globe attached to a blinker circuit for it to be seen by the D4... and then the reversing sensors will be turned off, setup for the trailer, etc.

I think that the Tow Pro sensors the trailer through load on the brake (blue) wire, and turns on the green (or blue) LED if calibrated or flashing if not. There is a technote on Redarcs website about some braking systems not being seen and you need to add a load resistor. My van has an iQ7 disc brake controller and I was worried that this would not be seen (before I got the new van)... but it is detected fine by the Tow Pro.

The diode needs to be inserted as per the circuit diagram above, but I do not think that this effects either of the above issues. If the diode is in the wrong way or mis-wired to the red wire... then the Tow Pro will not see the brakes being activated and do nothing... but the led should be on either way with a trailer connected.

Questions:
1) Are you using the original supplied cable between the Tow Pro unit and head? I used a 5m Cat 6 Ethernet cable ok.
2) Does the trailer have standard electric brakes?

Some fault finding suggestions to help work out what is wrong:
1) verify (with a meter) that the Tow Pro has supply +12VDC between the black and white wires.
2) the trailer brake lights work with a foot on the brake
3) the trailer brake lights work when the Tow Pro knob is pushed in

If all the above is ok... then either the trailer is not providing enough load to the Tow Pro to be sensed or there is a problem on the blue wire (which becomes D4 brown) through to pin 5.

For what it is worth. I have read through most of the instructions and even had a go at trying to get my arm up somewhere close to where the wires go through the Firewall. I decided to ask ARB in Brookvale, Sydney what they would charge for the unit installed. I was pleasantly surprised that I could get the Tow Pro fully installed including auto restart circuit breaker for $640. Done!

They installed the remote to the left of the handbrake, They were not to keen to go through the light panel that was my first option but I think it will work fine there. I have noted comments that it might be a little more susceptible to damages, spills there but I shall see how it goes.

LR Tow Pro.jpg

I have been following this thread for a while and finally installed the tow pro elite TBC today.

The controller works as it should. Brakes on horse float activate when the brake pedal is pressed. The only issue I have is the brake lights light up on the trailer but not the fog or side lights when the head lights are on. Any suggestions why this could be? I am using a twelve pin flat plug

Neat install...was it hard getting access to the panel where you installed the adjuster? And what did you bolt the control unit to?
Cheers

There is not much room on the light panel as it has a solid circuit board are back but it just fitted. The panel is little tricky to remove but worth it in the end.

The control module is fitted under the dash, it's hard to explain where it is. I will see if I can take a photo.

Just need to sort the park lights.

I found the problem and it is now fixed. Thanks to everyone who contributed on this thread as it made the job much easier.