where is the switch for the back up lights located

It's part of the transmission range switch on the side of the transmission. But check the bulbs first, i've found reverse lights, brake lights and headlights both burned out because of voltage spikes due to faulty battery terminal connections.

Just to add to Bob - if you have a manual transmission, there is a back up lamp switch located on the left side of the shifter cover. Sometimes the wiring connector can be loose or have a terminal issue.