none working laguna high level brake light the cure ?

I have a 1997 (P reg) renault laguna 2.0 rxe 5 door hatchback.
bought the car over 6 years ago and done me proud, but, i cant seem to find why the window mounted rear brake light does not work, there is the same number of wires on each of the tail brake lights so cant work out where the 2 wires from the window light go ?
is there a seperate fuse or relay ?
thought it would be simple to route new wires to the tail lights but route is not easy through the tailgate so fixing of fault could be better option....with the info, if anyone could help i would be grateful and thanks in advance !