Did you check the reverse light bulbs themselves. Check them first before checking the neutral safety switch. Also look at the wires in the trunk, on both sides of the trunk lock. Make sure they are connected.
Someone may have removed the key buzzer module, been inside the column and removed the contacts or they may have broken off.
Start inside the trunk also with the wires and make sure the fuel gauge wire is hooked up. Most likely it is the sending unit inside the tank.
Burnt out bulbs is a common issue for the gauge cluster. Replace the bulbs. Recommend LED bulbs. Others will most likely recommend the ones that work. I haven't done this upgrade as of yet to my fleet. Lol
The printed circuit after 50 or so yrs gets very brittle. Does your car have gauges? Idiot lights?
Hey! What year Monte and options do you have. Also, WE like pics!