Rear light cluster issue

[aquilaalba]

I should have mention this in the first place - I've replaced it with an automative bulb - slightly different as the contacts are more oval than round, but fits only one way and has two filaments. Still no joy. I thought that because if there was improper bulb fitted then there would be no continuity in the circuit - hence no light due to the fact the circuit is not closed. Will try to get at it today as soon as I'm done with all the work scheduled.