Grand Scenic electrics are horribly complicated i had a Renault tow bar fitted to mine by Reg Vardy Renault in Durham when i got the car 2 yrs ago and that even took them two days! What sort of sockets were on your factory tow bar electrics? The new 13 pin EUro single socket or the "classic" 12n & 12s arrangement? I'd restore it back to the state you bought it in as a beginning point and consult a tow bar specialist before it damages the car's complex electrical control systems.
Sorry if this is granny & eggs but 12S socket normally wires up like this:
caravan reversing lights (yellow wire : pin 1),
pin2 is spare
main earth (white wire : pin 3)
power supply to van for general use/ charging van battery (Green wire : pin 4)
pin 5 spare
power supply for fridge (red wire pin 6),
spare earth for fridge (black wire
With the engine running the car supplies electric to the van battery to charge it and keep the caravan fridge running while travelling - so some of the wires will be live when you turn the engine on! Also the spare pins 2 & 5 can be used for the van waterpump or blown air heating or if you'r van's really posh : electric toilet flush.
Sorry i can't help with the renault wire colours.
BUT if you have an electrical fire or blow one of the black boxes in the car consider the implications! Renault bits are expensive!
The Grand Scenic also has a sadly lousy towing weight. Its only 1300kg max with driver only in the car - passengers and luggage reduce the weight. Check your caravan weight - could it be too heavy ? Also check your van's noseweight (max downward load on the towball) it should be between 50 and 90kg. Some bathroom scales go up that, far if yours do stick a scrap of wood on the scale and set the caravan jockey wheel on the wood to spread teh load and see what sort of downward pressure the hitch is putting on the towbar. OK its not precise because teh jockey wheel is a few inches back from the hitch but for laymen its close enough . If you've not got beefy enough scales u can buy a noseweight checker from Barrons at Darlington, Catterick caravans,or Ropers that fits into the hitch head but once you've got used to loading your van you'll not need it again.