Um, most likely problem is in the switch at the base of the transmition stick. Auto right?
Well yea, there's a good how to on how to get into the VN-VS ones. It should be roughly the same! You sure it's just not the lights though or the cabling? Does the dash pick up it goes in neutral (if yours shows that)?
im pretty sure its a manual (look at his user name)
The reverse light switch is on the gearbox itself, should be on the side cant remember which side.
You could try unplug the switch then short out the wiring, see if the reverse lights come on, then you need a switch.
Otherwise the problem is elsewhere.
the reverse light switches are not a servicable unit just get a new one from holden they arent expensive
the switch is located on the drivers side of the gearbox all most at the top just jack up the car put stands under it get under the gearbox use a spanner to undo the switch, screw the new one in and plug the wiring into it and presto all done.
its a 5 min job to do as long as the engine and box are not hot