So i decided to wire up the side light bulbs in the top light clusters as only the bumper sidelights were working and in the dark it wasnt very well lit, so all i did was run a wire from the live on each bumper light up to the cluster light and bingo they all worked but now when the brake pedal is pressed with the sidelights on the drivers side cluster side and brake light go out, but if the sidelights are off all the brake lights work normally, so whats goin on chaps ?

Bad earth connection on the bulb showing the fault.
Check the wiring, but the usual reason is a poor connection between the bulbholder and the body of the bulb.

ok so i'm guessing your talking about the rear lights. my 96 disco had all the wireing in place it was just the light cluster unit itself that didnt have the wireing to make the tail light work just the break light. i added a bit into the cluster and made it work.

later i just got some 200tdi tail lights with indicaters too.

Ok ill check the earth thanks