As Iain stated I did not and do not have a multimeter. Instead of going down the route of buying a meter, a box spanner and maybe some loctite thread locker (not sure on this last thought) I took the approach of replacing the easiest part first- the pluggable sub-loom. Luckily for me this appears to have fixed the problem. 10 minute job which included removing the old one and securing the new one with cable ties. According to Iain and on inspection ( I can see where he is coming from) I also saved some skin on my knuckles as it is a right bugger to get to. Also I am apprehensive of screwing anything into the engine block in case I cross thread it! Location on the Sigma would suggest this is not an unlikely scenario for amateur like me! Mark