HELP! Bench Testing Vintage Car Radios?

How does one do this? All of mine are transistor, I don't have the equipment to deal with tubes. The first one I have is out of a 60s or 70s Valiant.

I have it hooked up and the light is on, for the first time in over 30 years! All I have to work with is a red wire, orange wire, green wire, and a black wire. There is also a jack for the antenna. I understand that the red is for power, black is for negative, green is for ground, and orange is for lights. But where do I plug the speakers in at?

:???: