Free lander reverse light help

I recently had the clutch changed on my freelander td4 Y Reg. The reverse lights don't work since it came back. Bulbs and wiring ok, changed the switch on gearbox but still nothing. If you press the switch in then the reverse lights work. It's something that makes the lights work in the gearbox. There is an inspection plate on the box but don't want to take it off incase springs and cogs fly out, so thought I'd check on here if anyone has any advice, thanks in advance