Here is my test kit. A simple AAA battery with some wire taped to it. Sometimes if I don’t have an AAA I’ve used RC car batteries, 9-volt batteries, and even the battery off my cordless drill. Be careful though, the higher voltage you use the more likely you are to damage the speaker. If you are testing the speakers you are replacing, then who cares, but if testing the new speakers it is best to touch the wire to it as short as possible to figure out the wiring. The factory plugs in the Jeeps are made to only go on the factory speakers one way, so figuring out which wire goes where is easy. If you mix and match speaker polarities, they will cancel each other out. Don’t get me wrong—you will still hear sound, but it won’t be as good as if you had all the polarities right.