Reversing lights

Hope this helps you abit,i owned a renault clio,and my reverse lights didnt come on,i changed the light bulbs etc,and then took the car to a mate of mine,and he jacked the car up and there is a switch,whats on the gearbox,and he got me a new one from the scrap yard,so perhaps its that,i think its on some kind of a plug,hope this helps let me know any way,Thanks Anne