Have found this:
Seat belt warning light
The SERV and AIRBAG lights come on its a common problem (almost every has it) its due to the wiring of the pretensioners going to an open circuit. Fiddle with the wires under the seat an the problem will go away.
On the early cars the solution is to look under each of the seats. You will see a grey connector.
On the passenger side disconnect it and cut the Blue and Brown wires off both sides. Then solder the Blue wire to blue, and the Brown to the other brown. Make sure you use insulating sleeves over the soldered connections..
Under the driver seat there are two pairs of wires in the grey connector.. Only cut the Blue and Brown wires and solder them together as above.. Reconnect the connector..
On the facelift cars it is ONLY the passenger side connector that is affected.. So again cut and solder the Blue and brown wires.
But its not the warning light, its the bleeps that tell you you dont have your seat belt on.
My last clio didnt have this so i figure its an option you can turn off...
Have been right through guides section, unless ive missed the thread you're referring to mate?