Can anybody help with this?
When brake and tail lights are both on, neither work on one curcuit. When just brakes, everythings fine. When just lights, everythings fine. But put the brakes on while the lights are on - nothing!

Any ideas??

earth problem?

earth prob pretty sure but make sure the terminals are touching as well on each globe holder... and the terminals are clean n free of crud....

also check that the s wiring isnt burnt n fused together in the s wiring harness..... usea multimeter and check by removing the wires from the light bulbs and applying power to one n see if the opisite wire is getting power maybe tahy have fuse together futher back in the harness..... trial n error.

Looks like bulb not touching actual holder and is earthing out badly. Will install new holder.

Thanks all