Connecting +12 wire from cargo trailer to Renault Grand Scenic IV fuse box

Hi all,
I installed a trailer hitch on my Renault Grand Scenic IV and I’m wondering where to connect the +12 wire. I found an empty spot in the fuse box which has +12V coming out of it, so I connected it there but now I’m not sure. The fuse for the trailer is is 15 amps and I’m concerned because I don’t know the gauge of the wire that feeds that slot (the back of the fuse box is not accessible enough so that I could figure out which wire is connected to that slot). I was wondering if such a connection is correct. I guess the question is if there is some standard of minimum wire gauge that feeds into the back of the fuse box?

BTW, the wiring is only for the lights of a small cargo trailer, not a travel trailer or anything…


Harness for trailer lights are not normally connected to the fuse box. The harness leads are connected to the appropriate tail&brake light wires giving your trailer tail lights, turn signals, and brake lights.
There are YouTube videos that show the process.


A safer install would be to use an inline fuse holder and attach to a 12v lug. No worries that way.

Four wires right? Ground, lights, right signal, left signal. Normally spliced into the harness at the rear were convenient. However on some cars now you have to use a control box that is plugged into the harness connector. I needed this for my Acura and git it from etrailer.Com. Don’t remember what paid for it but works fine and has its own fuse. Don’t know what 12+ you are referring to.

The wire found at the rear of the car for the left& right tail-lights is +12 v whenever the headlights are on. I expect that would serve the purpose of the +12 v connection needed for for the utility trailer.

Outside of Amazon UK I’ve yet to find a kit intended for Europe/Uk market vehicles similar to what @bing suggested, We’ve used essentially the same harness on a 2019 CRV that was plug and play other than adding a ground wire, had the Hitch shop at the local Uhaul install a hitch and wiring by Curt that work just as well as the same setup on our 2007 CRV.

If the fuse is located at the power supply end of the wire, you can connect it directly to the battery or a power junction point that supplies power to the fuse block of the car.

A cargo light doesn’t need a control box and shouldn’t be connected to the taillights.

Renault is not listed on their site. Evidently some cars use a separate wire for turn signals and brakes instead of using the same wire, thus the control box. For some reason others require a hot wire to be run. Sounds like 16 ga is standard, but sure if the diections say to run a hot wire to the connector, just pick a spot on the fuse box that is hot all the time. Who knows about the uk, or France, or wherever this is?

I guess it would help to know the rest of the wiring done. No trailer brakes assumed. Had one thought that was five wire with the fifth wire allowing using battery power while camped. Not smart to run your battery down camped in the middle of no where.

No power wire needed…

Thanks, appreciate all the replies!
I feel I was missing some details. I’m in France and ordered it off a French trailer hitch supplier website (france-attelage). Here’s a link to the installation instructions. It has a control box with a +12V wire, which should go to the battery. I guess it senses the voltage on the wires going to the vehicle’s lights and has some electronics inside to switch the trailer lights from the +12V wire to avoid drawing too much current from the primary wires. Now that I think of it, I should’ve connected it to a permanent +12V. Now it’s on +12V that is only on when the engine is running.
I found a Russian guy who shows how he wired it to the cigarette lighter on the back, which I think is +12V permanent and sits on a 15 amp fuse as well, so it sounds ok to me, what do you think? I don’t see how I can wire it directly to the battery, which would be optimal. So annoying you need to take apart half of the car for something basic like this…

I expect you are right, it should be connected to a 12 volt powered-all-the-time source. That way the brake lights will work even if key is in “off”, which is how the car’s brake lights work now probably. There are probably adapters available that make it possible to connect to near where the battery + cable meets the battery post, but that seems like an awkward wiring configuration. Seems better idea to inspect the car’s wiring diagram to find a better place to connect, probably there’s a spare socket available in the passenger compartment fuse box that you can insert a blade-connector.