stupid question

Okay, what am I doing wrong? I have two radios that I'm trying to bench test. I have them hooked up to a car battery, lights are working. I have a car speaker hooked up as well as an antenna. No sound from the speaker except crackling when I first touch the wires to the speaker. What am I missing? If its a ground, what would I be hooking that up to since I'm at my work bench? From where to where? I can't imagine both radios are bad. One is an am, the other is am/fm. I have the am/fm switched to am.