My mate had the same problem with his 89 32gtr lights didnt work when putting it into reverse but if he held the gear stick to the right they would come on so we new the bulbs were fine and just left it alone but this got worse till no matter how hard you pushed the stick to the right they wouldnt come on so got underneath it and bridged the wiring connector and yep they came on so we thought yep swicth is the problem so bought a new one from nissan about 80 bucks i think it was, jacked it up and yes you have to undo gearbox crossmember and drop the back of the box down to have any chance of fitting your arm up there went to undo the swicth and found it was loose and had been winding itself out it screwed in a couple of turns and what you know they worked fine when put into reverse but we put the new swicth in anyway seeing as it cost 80 bucks