Need some help - lights on my RS have now decided not to work.

At present the side lights work n/s and o/s and the main beam works n/s and o/s but the dipped (normal drving) beam does not on either n/s or o/s.

The bulbs are fine so what can it be ?

I assume it must be one of the folllowing

1) The wiring ! I assume this is not the problem as I would expect one side to work and one not work as I beleive each light is on a seperate circuit and would be a bit strange for both sides to go at once.

2) The indicator/light switch ! Possible - i have tried another switch which is old but as far as I know works and the problem is still there.

3) The relay on the back of the light switch ! Possible as I do not have another to test with.

4) The white relays/fuses in the fuse box ! Again as there are two relays I would expect maybe one side to work and one not too - again would have to be pretty unlucky for both sides to go at once.

Any ideas based on the symptoms as to what it is most likely to be ?

p.s. I may have answered my own question above but would appreciate some feedback to either confirm or deny !