66 t-bird radio

I have a 66 T-Bird radio I would like to test to see if it works ok so it has 4 wires coming from the side of the radio.
I expect the 2 black wires with a plug on the end to be speaker wires but I have a yellow wire and a blue wire also going to a plug.
If anyone knows I need to know which wire would be the hot wire that I can safely hook up 12 volts going to that wire to power the radio.

Thanks Rodney

I'm 99% sure the blue and yellow wires are The +12V for the radio, and display light (dimmer circuit).

Ground is through the chassis.

Originally Posted by jeffstar

I'm 99% sure the blue and yellow wires are The +12V for the radio, and display light (dimmer circuit).

Ground is through the chassis.

Thanks for your quick response, I will try it tomorrow.