Radio Testing

I would NOT use the typical battery charger, which most of the time has NO filtering, and outputs VERY dirty pulsating DC.

Unless it's stereo, you only have 3 or 4 wires........

Ground battery NEG to the radio case
Orange is the lamp
Red is battery POS
Carefully insert a scrap of wire anywhere from 6--10 ft into the center of the antenna, and hook up the speaker to the remaining two wires