All right, that's not too bad. I can bypass the copper and connect the wire straight to the bulb, leaving the earths connected where they should be. That works.
HOWEVER (You'll see a lot of these!):
There is no current reaching the wires in the ceiling. One of them (the purple) had a black coating on the stripped copper, which quite clearly would hinder conduction. I removed it; nothing happened. All right, I thinks, I'll replace that wiring.
HOWEVER!
Before I did so, I put the bulb to the purple and black wires that come directly from the (brand new and fullly functional) wiring loom, bypassing the wires run through the door pillar etc, which were the ones which I suspected did not work. Well, how nice. The bulb did not light when connected directly to the wiring loom. You understand, where I'd put the bulb there was no form of connection except pure copper wire (maybe more of the non-conductive stuff?
) between the bulb and the fuse and control boxes. No light though. 
HOWEVER:
I found that the upper fuse had gone. Replaced it, problem solved. All other electrical functions in the car work.
HOWEVER!!!
The two * wires from the fuse and control box- the purple and the black- still fail to light up the bulb.
So far, then, one may ascertain that the bulb works, the battery works, and everything else is a failure, but only with regard to the roof light, since every other function in the car works off the same loom. What can I do?
Where could the problem lie?
Actually there is one thing; in the control box the right-hand coil does not make any form of contact at all at the top, and there is a huge clearance between contacts, while the left-hand one is making contact, and has only a millimetre or two of clearance. Is this normal?
I think that's everything I feel!
Simple pleasures for simple minds, I suppose!
)! It's good to be back.