Thread: How does the connection of a Trailer/Caravan get sensed?

Originally Posted by StewG

The Disco rear sensors (in reverse) are driving me mad because it does not disable despite having a trailer attached. The van has LED lights. Should I add a load resistor so that the "lights" draw more current if the sensing is done via the lighting circuit?

A pulse is sent down the indicator wiring of the 'black' trailer socket. If the appropriate resistance is detected it assumes a trailer is connected and disables reversing sensors plus enables gear box adaptations. LED indicator lights do not have sufficient resistance for this purpose so the presence of a trailer is not detected. Yes, you need to install at least one load resistor in parallel with the trailer indicator LED lights.

There is a long thread somewhere on it all. Just don't get confused about it all - the D4 behaves differently to the D3. The D4 only requires load resistors, the D3 requires load resistors plus further measures to properly handle LED trailer lights. These differences are not always made clear when people talk about this.

As for power to the van, others can take that up but I think you will find the power lines in that 'white' socket to be not adequate for your needs due to the relatively low current rating of that circuit. Dedicated circuits to the vehicles auxiliary battery maybe required.

White socket pin 6 is IGN/engine run and pin 4 is permanent supply. Run the ESC from pin 6 and van battery charging from pin 4 although a high current connection is preferable.

Thanks to both Ferret and Graeme. It is all coming a bit clearer. I'll try a few different resistors or globes in parallel with LH or RH indicator wire to ground at the van and see what happens. As for the ESC and Charger, I think I'll remove the original white plug and just run new wires (with in-line fuses) direct from the battery to Anderson plugs at the rear. I've seen a similar arrangement somewhere in this forum. I recently bought this MY13 second hand and it has already had a RedArc fitted and some changes to the wiring at the rear. I'm still trying to figure out exactly what is changed, but the 7-pin black plug seems to do the right things.

Make sure you check the actual outputs for each of the pins on the 7 pin black plug. My MY13 Disco had a previously installed brake controller but somehow had the brake light & brake pins reversed. I needed to correct the wiring and install the diode that had been missed too.
I ended up having to wire in a Narva 21W load resistor for each of the left & right indicator as well as brake & tail to stop the Jayco van LED lights from flickering as the D4 pulsed the circuits to check the lights.

I have a D4 16.5. I also have a caravan with LED lights and indicators. I thought I might need the resistance wiring. But I dont. Once I connect the plug it cuts out the rear camera and the sensors. Perhaps the later D4's are wired for LED's just like their rear lights. In regards to wiring up extra 12V. I use the Traxide anderson plug. then I piggy back two extra anderson plugs. one is a red one for the anti sway, one is for the 12V fridge, and one is for fridge detection and the breakaway. I dont use the white plug at all.

I have wired up a Caravan, boat trailer and box trailer. The last was the box trailer. I did it because I have a long driveway and when reversing the noise was annoying. I did it in a few minutes. I had some cheap resistors from the net (ebay). I stripped the wire near the left and right indicators. I soldered a resistor green one end and white the other on right side and on the left (other side) yellow and white. This gives the resistance required. Not fancy but works.

I have wired up a Caravan, boat trailer and box trailer. The last was the box trailer. I did it because I have a long driveway and when reversing the noise was annoying. I did it in a few minutes. I had some cheap resistors from the net , stripped the wire near the left and right indicators. I soldered a resistor green one end and white the other on right side and on the left (other side) yellow and white. This gives the resistance required. Not fancy but works.

My 16.5 also has a button on the dash to stop the reversing beep, but still leaves the camera active. My beeper goes off as soon as I hit reverse due to the tyre on the back. The camper has LED lights, but we have no problems with them at all, other than two wires being connected to incorrect pins by the installer thus resulting in no brakes or lights for the trailer. We desired the adapter I use, and now all good. When we get the new van plug put on later, it'll be sorted properly then.