Thought I'd update thread seeing there are at least two replies (tnx to those replying).

After the first reply, I tried soldering the loose wire onto the terminal on the pcb that I thought it belonged. 
Riser didn't work any better.

In the meantime I had emailed Cablesaurus, and they advised that If there was a cable loose, it was probably damaged in transit, and they offered me a replacement product or a refund.  I have accepted their offer of replacement product.

In the meantime, I saw a UK based post from someone doing risers in the UK.  I've ordered a couple of the UK risers.

So if all goes well, at some point I'll have 3 new risers, and can either find a fix for this old one or trash it.  I'm more likely to trash it. 

Thanks for the replies to this thread anyway!