Thanks for the replies folks
I have resigned myself to having to rebuild the loom. I'm off work this week so I will strip it down tomorrow (with plenty of pics and labels) and set it out on a board.
I'm not sure how much change the PO has made to it, so once stripped I will compare it to the wiring diagram to see if a standard replacement will work or make my own.
If the latter, then no doubt I will be on for more advice on stockists, connections, type of wiring etc