REVERSE LIGHT HELP PLEASE

Being new to mk1's, caddy's and diesels plus knowing sod all about cars in general could someone please explain where the reverse light switch is as i have no reverse lights.
I have a 1988 caddy 1.6 diesel
many thanks
Pootz

Mines on the gear box (Cabby with mk3 gear box), Check the earth to the back light clusters and cabling before trying a new switch.

cheers, earths are working fine as checked them out and replaced bulbs

ya top of the gearbox. black and black/blue wire, bridge the wires together with ignition on and the reverse lights should come on. if not the fuse or wiring is at fault, if they do its the switch