1995 Plymouth Voyager taillite

You can get a 12 volt circuit tester at the auto parts store. It looks like an ice pick with a wire coming from it ending in an alligator clip.

With the lights turned on, clip the wire to the "hot" side of the circuit (the black/yellow wire terminal jdl mentioned), and touch the probe end to the black ground wire terminal and see if it lights up and/or buzzes or whatever the tester does. If not, ground instead to a clean, unpainted surface of the car's body or frame. If it works now, your ground wire is broken or loose somewhere. If neither, then your hot wire is broken, loose or shorted somewhere.

Check the fuse by opening the compartment below the dash, finding the right one from the diagram inside the cover, and pulling it out (with the power off). If it's blown, you'll see the metal inside the clear plastic is broken.