[urq] No start situation - suddenly

[Keith Lloyd]

Over the winter I had the old girl resprayed and since then have snatched only odd moments of free time to put her back together again, replacing the cam belt and radiator at the same time. I filled the system with water to check for leaks, fired her up and made sure everything worked - which it did. Since then I have refitted the bumpers and lights and now suddenly she wont start.
I am fairly confident the problem is lack of power to the fuel pump - obvious sign - no sound of it priming when switching on ignition. To check this I worked backwards: 
I have a supplenetary relay set up to provide the fuel pump with the full voltage so the wiring is all in place to test the pump with a direct feed from the battery. I can confirm that the pump works by giving it a direct feed from the battery..
I tested the relay (the supplementary one mentioned above) and this works fine but is not receiving any power from upstream. I have tested the actual fuel pump relay (relay #10 in the fuse box - part number 857951253). This works but is receiving no power to trigger it. 
The fuse (#13 - 15A) This is fine and intact.
However there doesn't appear to be any power reaching terminal the fuel pump relay. Looking at the only wiring diagram I have (which is for US spec quattro - from Bentley) shows this relay to receive it's feed from #15 which I understand is the ignition switch. I naturally thought that perhaps the ignition switch had stopped functioning. But checking the only other items that take a feed from here (reversing light and feed to coil), they both work. The problem seems to me to be somewhere between the ignition switch and the fuel pump relay. Where though, I have no idea. Any suggestions will be gratefully received.
I have done no work in or around the fusebox area nor under-dash. The only work I have done is at the front (refitting bumpers and lights and refitting rear bumpers. Is there any wiring here that has anything to do with the feed to the fuel pump relay. I can't imagine so but, like I said, any suggestions will be most welcome.
Many thanks in advance.

Keith

'87 WR