Rear light question

Turn the key to the on position, put shifter in reverse, go to the trunk remove the bulb should be a single pin socket. check for 12 volts with either a volt meter or test light. If you have power, most likely bad bulbs or no ground. If you have no voltage there, its the switch in the transmission. Remove the plug, should be a 3 wire, one for the neutral safety sw and 2 wires for the back up lights. Check the harness there, for 12 volts, one wire should have power. If you have 12 volts there, then its a bad switch.