Think I have made some progress. Your comment about 'gear selector lamp' made me think the empty plug is for a column shift so power must be elsewhere. Had closer look at wiring diagram and looks like dash light wiring is linked to radio plug where there is a red and orange wire. My radio is missing and had a look at the wires and they had been cut and left hanging. I joined them together with a 10amp fuse and now dash lights go. Only thing is that they light up when you turn they key , even without turning the headlight switch on.
Thanks 74challenger03 and Chris,
tony