We rewired and it seemed to do the trick, for a few hours. The reverse then again refused to come on. So figured it must be whatever triggers the switch. It must be worn down. We put a spot of weld on the end of the switch and ground it smooth and hey presto its been working for two months now. Im not suggesting anyone else try this as ther is a possibility that the weld will break off into the gearbox but the alternative as far as I saw it was to open the gear box and replace the offending part there.