radio wiring question...know these wires?

[dbenamati]

I wanted to know if someone who knows radios can help me with a Delco AM/FM radio question about the wires comming from the radio (it may be from early 70's chevy radio) There are three wires that are not speaker related (yellow, gray and black) can anyone tell me which is the power wire to the radio? My guess is yellow but before I blow the thing up, thought I'd ask. also if I were to test using a 12 V. battery with a fused link, do I have to ground the radio through the housing or is one of the other 2 wires a ground? Thanks, Dave