Rear lights issue

[PJG]

Hi, I've an odd problem with my rear lights. When I turn the lights on my right side brake light stops working. When they are off it works ok but the left hand doesn't. Also with just the lights on (not using brakes) the left side is ok
but not the right. I hope this makes sense.

Any ideas would be appreciated.

Thanks

[Trooper]

Changed a bulb recently? not unknown for replacements to have the filaments configuration wrong, particularly unbranded bulbs from little shop on the corner. Could even be the wrong bulb if one of those helpful assistants in Palfords did it! If all else fails after checking sidelamp and brakelight bulbs (don't forget it is the same bulb!) check the earthing to lampholders and assemblies.

[PJG]

I think I've sorted it. I've fitted some replacements that I bought from roughtrax the other day.
I replaced both sets, now they work as should. Only thing is the left is slightly brighter when applying the brakes