I have added a reverse camera on the rear of my trailer. And I have added a normally-closed relay to switch off the camera on the rear of the car when a trailer is connected. My problem is to find a wire which can control the relay. I have tried to wire into the trailer ground cable curcuit, but then the ecu sensed that there was something wrong and shut down all the lights on the trailer.

What I need to find is the signal cable that tells the parking sensors to shut down or similar functions, and tap into that curcuit. My car is a 2004 td6.

I would be very grateful for ideas

The trailer electrics work on the brake lights, when you plug in the electrics it senses a greater load through the brake light circuit and then it does its stuff (through the various ecu's). If you were to cut the wire to the break lights in the trailer plug then the car would not know there was a trailer on the car...


I hope that helps...



Craig

Outrageous idea - but how about controlling your relay from the reversing light (on the trailer) ?

Thank you for the ideas. I will test them out. I don't want the relay on the trailer, but if no current is sent to the reverse lamp on the trailer unless there is extra load on the brake light curcuit, then I can tap into this wire between the trailer ecu and the socket. ----------
2014 tdv6 (ex. 2004 td6, 1997 2.5 dse)

When you select reverse +12V goes onto the trailer reverse light connection in the 12S socket whether you have a trailer connected or not.
I checked this when I was considering using the connection for supplementary reverse lights on the car.

Thanks Nicedayforit. Then I'm back to where I was.

Any ideas are greatly appreciated! ----------
2014 tdv6 (ex. 2004 td6, 1997 2.5 dse)

There is one possibility concerning the rear parking sensors.
When you select reverse with a trailer connected the rear parking sensors don't operate.
It may be that you could use this switching function to operate your relay.
I haven't had time to look at this in detail but in the meantime you might like to look at the wiring diagram below.
I'm not fully sure how it functions but I think there may be two possibilities, the parking sensors ecu supply and the parking sensor sounder.
It might be possible to operate a very small relay off either without upsetting the ecu and use the contacts of that relay to operate the larger relay coil serving your camera.

Click image to enlarge

Reverse lights are probably the best bet; just don't use a relay, at least not directly.

A transistor to switch the relay on would isolate the reverse light circuit from the relay draw.
I don't know how sensitive the FETs are in the BECM; they might not notice a transistor, whereas the current draw for a relay coil is close to the same as a lamp. Jim
2000 NAS HSE
2005 NAS HSE

Thanks again for your ideas. From Rave it seems like PDC is controlled by canbus and with my knowledge I don't think I should fiddle with that.

I like the transistor idea. I have never used transistors so I hope you can help me with some further instructions. The wiring diagram shows where I added my relay. On the ground side, as there will only be current when a socket is connected. Can a transistor terminal just be spliced in there? An example of what transitor to use would also be greatly appreciated.

There is of course the simplest way of all, guaranteed to work, the manual on/off switch.