Those old mopar electrics are pretty simple (don't let that rat's nest of a wiring diagram fool you). Think of electricity like water flowing through a pipe, and you're good to go for about every electrical problem in the car. The water pressure corresponds to voltage, and water flow corresponds to amperage. The battery is the source of the water pressure, it's like the tank up on stilts in a small town. The water wants to flow from the tank to the ground.
If your lights aren't working, it's because there's either a break in the water pipe going to the bulb, or a break in the pipe going from the bulb to the ground. With a voltmeter, you can see the pressure in the wires.
Pick yourself up a cheap multimeter from Radio Shack, and you'll be good to go for debugging it. Sometimes it's easier to use a test lamp to check for voltage, or even a buzzer, if you'll be tracing wires while upside down under the dash!