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Just fitted a towbar plus an original Renault harness (13 terminals). Problem is that the trailer connector is completly dead. Not a single volt anywhere... I even hooked up the red wire which can supply continous 12V - nothing. Ground connection is ok, and all the lights on the car works just fine. If I unplug the trailer box, the rear indicators no longer works. So something in that box is apperently working... I'm running out of ideas, anyone else who have had a similar fault?

Does that not suggest a wiring fault?

When you say you have used an original Renault Harness, I assume this was Brand New and you have fitted it yourself?

Not having fitted one myself, did you have to modify existing car wiring or was it just a plug connector?

Yep, it's brand new and I've been fitting it myself. No modifications were necessary, it's just a matter of pulling apart the existing connectors and plug them the into the harness. At the rear lights there are two Y-connectors, one goes to the existing cable and the other plugs into the rear light.

swefrix wrote:

Just fitted a towbar plus an original Renault harness (13 terminals). Problem is that the trailer connector is completly dead. Not a single volt anywhere... I even hooked up the red wire which can supply continous 12V - nothing. Ground connection is ok, and all the lights on the car works just fine. If I unplug the trailer box, the rear indicators no longer works. So something in that box is apperently working... I'm running out of ideas, anyone else who have had a similar fault?

You say that if you unplug the trailer the rear indicators no longer work, I assume this is the car ?

I would suggest going back to the start and reconnect the electrics in the car as it was when you started and check all is working.
You say you have connected a 13 pin socket, I'm sure it does not make much difference, but I notice that you appear to have only downloaded instructions for 7 pin?
Which towbar have you fitted, Retractable or Swan?
What are you using to check the socket, multimeter or something else?
You can get socket testers from Amazon, UK Amazon is here https://www.amazon.co.uk/Electric-Trailer-Plug-Tester-Pin/dp/B01FNXJB7Q/ref=sr_1_1_sspa?keywords=Trailer+socket+tester&qid=1559708543&s=gateway&sr=8-1-spons&psc=1 as a guide when looking at Amazon relevant to your country.

It's a swan neck towbar. But I wrote "If I unplug the trailer box" (that's the small electronic box which is part of the harness), then the rear indicators on the car stops working.


The main purpose is to disengage the rear parking sensors when a trailer is hooked up. But as you can see, it contains quite a lot of electronics. I downloaded the PDF for the 7-terminal harness just to compare, but there is no difference in the actual connection compared to the document supplied with the harness. Since the connectors are all different, it's practically impossible to do it the wrong way. Worst case is probably if you mix left and right side cables up at the rear lamps.

The harness for a 13-terminal connector (which is the only available from Renault, according to the dealership...) contains two extra cables, one yellow and one red. They are supposed to deliver +12V to a camper, the red has continous 12V while the yellow is only active when the ignition is on.

I've used a multimeter to check the voltages, don't have access to a socket tester, and I'm a bit reluctant to buy such a device just for this. I'm more and more convinced that there's something wrong with the box, but it's practically impossible to try and measure it.

Maybe it's a bit unusual that people do this type of job themselves on modern cars, but the suggested price at the Renault workshop was just ridiculous...

Adding this harness requires a configuration change of the car ECU, there is a parameter called "Configuration Trailer Present", but that was fixed last week when the car was at the Renault workshop for another issue.

It turned out there was a cable in the cars own harness (with constant +12V) which must be attached to the trailer harness. Hard to find, it was more or less hidden under a black insulation tape. Once this was connected, all lights on the trailer works ok.