Probably the reverse light switch. They have a hard life living in a hot oily environment. Had to change mine last year as it is now a fail on the MOT if it don't work. Quite an easy job to do, remove rubber boot and gear stick (its a quick release stick), remove carpet & insulation, take transmission tunnel cover off, change switch. I used an Intermotor switch which cost a few quid and has proved reliable so far. Job took a couple of hours including coffee and fag breaks and dicking around looking for tools.