Is there a way to test a radio off the car? I took the old ratio out and hooked up the second hand replacment but it won't turn on, ie won't light up. So I hooked the old one back up and it won't turn on either. So I used a voltmenter to check the power line on the car was good (both the always hot and the key-on/ACC hot wires) and I connected just the power and ground but neither radio will light up. I trieed the ground wire and grounding directly to the metal the radio scews onto. I have a battery charger. Would it be safe to use that as a power source to test if the radios light up? Other ideas? I don't need to connect the speakers yet, just see if the radio powers up.