Thread: D4 Electric Trailer Brake Wiring

G'day Sneigy

I had a TowPro fitted recently to my 2012 D4 & after some initial teething problems, I took my Tvan for a two day run to try everything out. At first all was Ok. I used the TowPro in the auto mode (blue led) on the road & then changed to manual mode (green led)for some steep bush tracks. All went good. When back on the blacktop again, I tried to change the TowPro back to manual. The TowPro indicated a fault code. (Redarc suggested the code could be no stop lamp signal)I had no trailer brakes or trailer brake lights at this stage. On arriving back home I found there was no power at the car socket on pin 6 (stop lamps). I hope you may be able to help me here. I have not been able to find the source of supply for this circuit. The hand book does not seem to list it in "fuses." The brake lights on the D4 are operating Ok. Have you got any suggestions as I have hit a brick wall here.

Phil

Hi Phil,
I would be checking the brake wire pick up feed.
If they have fitted it correctly the pick up "Should" be done in the L/H rear cargo area. If it has been connected at the brake pedal switch you will have issues.
Don't have the wiring diagram in front of me but i think the later models use "Fets" & not fuses.
Also check the Circuit breaker it also "Must" be a 25Amp unit.

HTH Cheers.

Do the other trailer lights work? If not i'd be looking at the trailer ecu (sneaky fuse hidden inside) as if the didn't put a diode or relay on the pickup from the stop light circuit there could have been a reverse current

Originally Posted by sniegy

Hi Phil,
I would be checking the brake wire pick up feed.
If they have fitted it correctly the pick up "Should" be done in the L/H rear cargo area. If it has been connected at the brake pedal switch you will have issues.

Why is this so? Looking at the wiring diagram it is straight through from the switch to the lights. I have connected my Tekonsha at the switch and have had no problems.

The Trailer wiring has its own circuit. It does not run off the same as the brake switch. When the brake is supplied the CJB then sends a signal from the Body control module to the trailer wiring to work.

If you have an issue with the brake switch it can cause false trailer signals.
If you have a short circuit in your Tekonsha you will fry your CJB directly.

Cheers

Thanks Sniegy, Geedublya & Meken,

All the other Tvan lights are working Ok. Its only the stop lights & brakes not working. All is Ok with the Tvan. I had a mate hook his car up to the Tvan & all lights & brakes worked.

So the problem as I see it is no brake signal in the D4. Sooo.. that means the TowPro cannot operate as it has no brake signal. The problem seems that the brake signal wire that was working is not now & I can't find the point of supply to that wire(red).

Sneigy, it has been wired a bit differently to your way. They have run two wires(a pair in a sheathed cable) from the TowPro along the top of the left chassis rail around to the back of the black socket. The brown wire (pin 5) is cut back approx. 50mm. The red wire( Trailer brake lights pin 6) connects to one of the wires to the TowPro. (brake signal) The other wire from the TowPro (controlled braking)connects to Pin 5 on the Trailer socket. ( I hope you still with me here). CB is 30 amp.

I'm just mystified why the power has disappeared & where it is supplied from!!!!

It was all working Ok, then.......?

Phil

Originally Posted by PJJ

Thanks Sniegy, Geedublya & Meken,

All the other Tvan lights are working Ok. Its only the stop lights & brakes not working. All is Ok with the Tvan. I had a mate hook his car up to the Tvan & all lights & brakes worked.

So the problem as I see it is no brake signal in the D4. Sooo.. that means the TowPro cannot operate as it has no brake signal. The problem seems that the brake signal wire that was working is not now & I can't find the point of supply to that wire(red).

Sneigy, it has been wired a bit differently to your way. They have run two wires(a pair in a sheathed cable) from the TowPro along the top of the left chassis rail around to the back of the black socket. The brown wire (pin 5) is cut back approx. 50mm. The red wire( Trailer brake lights pin 6) connects to one of the wires to the TowPro. (brake signal) The other wire from the TowPro (controlled braking)connects to Pin 5 on the Trailer socket. ( I hope you still with me here). CB is 30 amp.

I'm just mystified why the power has disappeared & where it is supplied from!!!!

It was all working Ok, then.......?

Phil

OK Phil,
I will assume it is just a twin core sheathed in black PVC with a red & black wire inside that is run to the rear.
From the Tow Pro Module the red coloured wire is the brake light pick up & that should be "Connected/Soldered" to the wire that goes to pin 6. (Nothing should be cut)
The other wire at the Tow Pro end is a Blue wire & this should be connected to the wire that is in pin 5. The brown wire that has been "cut" back 50mm at the plug end.

Using a Multimeter check that you have a brake light supply in pin 6 of the plug. This will tell you if you have a supply where you require it then..
Check the pick up wire on the brake circuit. Make sure the connection is good & proper.

HTH Cheers

G'day Sneigy


I spent all yesterday arvo reading this Thread. Up to about Twenty something of the 36 as I write this. It's amazing whats in there.

Today I have been going through the whole wiring job that the mob in Canberra did for Me. Pulled out the battery & checked the lot & drew a circuit diagram of the wiring.

So here are my findings -

All the wiring is wired correctly. (not a very high standard but)

All the connections are Ok

I have tested for a brake signal (Ignition & foot brake on) & there is none. Interestingly, my analogue multimeter was picking up a very small "pulsing. (mV)

When reading through the thread, I did however see your "important update" about putting a diode in the Red wire from the EBC. This has not been done.

At this stage I'm thinking my problems are from this important omission in the wiring. I hope it hasn't fried something!

I should be getting an appropriate diode later on today, so I can wire that in tomorrow.

I also read on the thread somewhere, (can't remember who posted it) that they had exactly the same problem that I have now. He also said that the dealer needed to replace a relay?

Thanks for the time you're spending on this with me mate. It was really starting to get me down a bit.

The closest L.R. dealer is about 250klms away, so I,m trying to sort this out myself, with help from you guys.

Also, I'm doing a Vic High Country Trip with some friends in the 1st week in December so the pressure is on a bit. I couldn't imagine going in there with no Brakes or Brake lights on the Tvan

Got any more suggestions?

Phil