Some years ago lamp failure came on repeatedly with no bulbs failed and isolated to rear newriside cluster dealer gave me new lamp holders free. then it started again and he said cluster had to be changed - fixed problem. Now same problem on offside rear this time I removed cluster to try and identify fault/ open cct. Found to be that if the pink (brake light holder is lacked in fully - rotated to the right the earth wiper comes to the end of the contact plate - falling of it. Design fault. Turning it back a few degrees solves the problem.