Thread: D4 Electric Trailer Brake Wiring

Hey Gordon,

See answers in red below. Scott dropped in to my place today and connected his car to my trailer and everything worked perfectly, all trailer lights and the brakes. Then connected up to my car and the brakes dont work, but all the lights do.

Originally Posted by Nod

Howdy Geoff,


1. D4 not recognising trailer
The trailer LED lights are not sufficient load on the blinker circuits for the D4 to detect it. You will have to add a NARVA 21W load resistor across either (or both) blinker circuits at the trailer to increase the load. All trailer lights work fine, connected to the D4. Even the brake lights work when pushing the Tow Pro Knob
When you close the drivers door the D4 sends out a pulse on the indicator circuits to try and sense a trailer load, this is the LED flash you are seeing. Your trailer does not present enough load to be detected. Only one load resistor is actually required.... some of us like symmetry.
There are many threads on the forum detailing various methods to install the resistor(s) Should this cause the Tow Pro not to recognise the brake load though, as the lights work perfect.

2. Tow Pro install
Looks as if you are very close... as far as I can ascertain... the wiring looks correct (diode orientation)... your wiring diagram is fine, though the diode picture is unclear with an additional line.
Breathing is good.
Lighting up/detecting the trailer attached is good.
Braking and pushing the Tow Pro button turning on the trailer brake lights is good.

"Whenever i close any door, it illuminates the camper brake lights!"... means that the brown (pin 5) and black (pin 7) wires are swapped. These are the 2 wires that are at joined at the splice in the rear cubby Scott came and we checked his D4 and it did the exact same with the Trailer lights when doors are closed. His vehicle worked perfectly with my camper attached
Is the tow plug the original 12N & 12S or has it been changed to a different connector (7 or 12 pin flat)??
You need to check that the brown goes to pin 5 and the black to pin 7. YES. Although i think that my splice wire colours may be the issue. Mine has a single Brown wire into a splice joint, then Brown and Black out. I cut the Brown wire post splice and then connected to Blue/Black from the Tow Pro. How do i check if the Brown wire goes to pin 5?

Attached is a diagram that may help.

Regards,
Gordon

Howdy Geoff,

1. The indicator lights will still work even if the D4 does not actually detect the trailer (green indicator flashing with the indicator).
The car detecting the trailer supposedly sets up the car for the trailer load (turns off rear sensors, blind spot monitoring, changes shift points, etc.)
This has nothing to do with the TowPro.

2. The best way to ensure that you have the cables going to the correct pins (5 & 7) is to use a multimeter (ohm setting) to continuity check from one end to the other. Stick one of the meter probes in pin 5 and check if it is the brown or black in the rear cubby. Then check pin 7. This may need a additional bit of wire to be added on the end of a probe to extend the length.
The TowPro looks for load on its output (blue).

Regards,
Gordon

Thanks Gordon,

Ill check tomorrow night and advise. Lots of hair pulling, however on the positive, im learning LOTS about my D4

cheers
Geoff

Originally Posted by Nod

Howdy Geoff,

1. The indicator lights will still work even if the D4 does not actually detect the trailer (green indicator flashing with the indicator).
The car detecting the trailer supposedly sets up the car for the trailer load (turns off rear sensors, blind spot monitoring, changes shift points, etc.)
This has nothing to do with the TowPro.

2. The best way to ensure that you have the cables going to the correct pins (5 & 7) is to use a multimeter (ohm setting) to continuity check from one end to the other. Stick one of the meter probes in pin 5 and check if it is the brown or black in the rear cubby. Then check pin 7. This may need a additional bit of wire to be added on the end of a probe to extend the length.
The TowPro looks for load on its output (blue).

Regards,
Gordon

Gordon,

Im also going to Download the wiring diagram from Topix, so that should help.

cheers
Geoff

Originally Posted by Nod

SNIP

"Whenever i close any door, it illuminates the camper brake lights!"... means that the brown (pin 5) and black (pin 7) wires are swapped. These are the 2 wires that are at joined at the splice in the rear cubby.
Is the tow plug the original 12N & 12S or has it been changed to a different connector (7 or 12 pin flat)??
You need to check that the brown goes to pin 5 and the black to pin 7.

Attached is a diagram that may help.

Regards,
Gordon

Hi Gordon,
Do you mean the 7N & 7S plugs? If so, the useful table also needs to be updated.

Best Wishes,
Peter

Thanks Peter. Yeap noticed this a while back... and "break" instead of "brake".... but only have a bit map now.... one day!
Gordon

Originally Posted by Nod

Thanks Peter. Yeap noticed this a while back... and "break" instead of "brake".... but only have a bit map now.... one day!
Gordon

Hi Again,
How did you draft the table originally? If it was Excel, I could redraft and forward it to you.

Best Wishes,
Peter

Hi guys,

well after scouring over the wiring multiple times, i decided to run my hands and eyes over the brown wire from the rear left cubby to the plug. I could get power to the cubby, but nothing at the plug. I removed the rear left tail light and there staring at me was the culprit, the brown wire had been pulled out of the connecting plug!!! I connected and soldered it back and and presto, the Tow Pro blue light illuminated when i connected the trailer . The remote was flashing green on auto, but stayed solid green when i switched to manual, so it needs to calibrate tomorrow and then it should be good. The only thing i will do now, it go back over the wired joints and solder them all, take away possible weak links.

Now to wire in the resistors for the LED trailer lights and all is good. Thanks to everyone who gave their input and suggestions, particularly Gordon and Scott, who dropped in to my place on Sunday.

cheers
Geoff