I had one of these fail today surprisingly. After discovering there was no offside rear indicator today I checked the obvious, the bulb which appeared to be fine gave it a wiggle as you do, nothing! Checked connections under seat then with multimeter checked for power at bulb socket which showed power supply ok. Soon became apparent that there was no earth to light. The culprit was the earth/bracket mount (thingy). A few taps with the hammer on the rivet and it now shows good connection. I will remove rivet at some point to clean connection before riveting again.