Take it to the garage.
There is a backup switch in the gearbox. When you shift into reverse, the gear box switch contacts the switch and lights the white reverse lights. If you find that the reverse lights don't work it could be that the switch is not being triggered by the mechanism inside the gearbox. This is providing that everything else is working; wiring,bulbs,etc.
I believe they are grounded through the system wiring. If you're having trouble with the brake lights not working, it's might be the signal switch assembly, under the steering wheel; a difficult R & R.
Check to make sure that the starter wiring has been properly installed.
Check bulbs?
sprak plug wiring diagram chevrolet lumina 1996 3.1
If you do not have working tail lights on your GMC vehicle it may be an issue with the wiring or your lights may be burned out.
if the bulbs are not bad, it is the fuse, if the fuse is good, its the wiring.
Check the fuse or the wiring
It is important to have working brake lights on a vehicle. If the brake lights are not working a person should first check the fuse, bulbs and at last the wiring.
Working fog lights are important to have a car for safe driving. The wiring diagram for the fog lights of a Toyota Avensis can be found in the maintenance manual.
If there is a trailer wiring harness on the vehicle for towing unplug harness under drivers side rear tail light to eliminate the trailer wiring that's probably the issue then plug factory wires together
If the brake lights are not coming on in your car and you have changed the bulbs and the fuses with no results, you could also check the wiring in your '98 Chevrolet Lumina. The wires may be damaged or even broken.