It's not beyond the scope of the DIY-er, though the 12S feed is a bit of a nightmare. Realistically, you need to run a 12v feed through trunking along the underside of the car and into the boot, you can then use this one wire to supply a voltage sensing split-charge relay.
The rear fog and reversing lights are in the boot lid on the hatch, which means you have to get these feeds from elsewhere. I've previously posted some pictures and details of access here. Sport Tourer owners are luckier, as these lights are in the main clusters.
Bolting the actual bar on is straightforward enough, though some kits are easier than others. Just be sure to follow the instructions carefully and tighten everything to the recommended torque settings. If you go for a flange style ball, then the ball to bracket bolts have to be torqued to a setting that's off the scale on most torque wrenches. It might be worth bribing your local friendly mechanic with the price of a pint or two to torque them correctly once you're done.
Edit: Sorry, wrong link. Try this one http://www.renaultforums.co.uk/elect...nt-wiring.html
Further edit: There's debate over whether bypass relays are required for the road lighting. I've never bothered on either of mine, and the official Renault wiring loom is basically just a bunch of wires with what appears to be a bog-standard trailer flash relay in it. The concern comes from the possibility that some or all of the Lag's lighting is run via a multiplex controller. While I don't believe this is the case for most of the lights, it does appear that the indicator outputs are controlled by the
on most modern Renaults.
The upshot of this is that seriously bad wiring on the trailer could, potentially, fry the
(read VERY expensive.) In practice, I still consider it very unlikely, but ultimately it's up to you.
If you're going to run bypass relays, then power them from the 12S feed that you'll be running from the engine compartment. Don't source the power feed from elsewhere, as this can cause you other problems. I know Hondo has first hand experience of this.