I drive around in a 1987 Chevy pickup with a dump body for work. I’m trying to get the radio working. There are 7 wires out of the radio. I had assumed 2 wires to each speaker, 2 wires for power, and the antenna. But now it seems that both channels share the green wire and the orange wire is for something else. Does that sound right? What is the orange wire for?
Typically, the wiring for a lot of aftermarket radios is for 4 speaker wires (green and green w/ stripe, grey and grey with stripe) and 3 power wires (12V constant (blue), 12V switched (red), and ground(black)). Antenna socket is separate from these. I say aftermarket, because factory radios of this era typically have a connector for the wire harness, not wires sticking out of them.
Ahhh, that makes sense. The Orange wire is just so it doesn’t forget the time and presets and stuff when the truck is off. This radio we’re talking about doesn’t have knobs or half of it’s buttons or a display that works, so the presets are the least of my worries. I can probably leave that alone. 
I’m still short a speaker wire. I’ve never heard of two speaker circuits sharing a wire, but that seems to be the case. If i put a speaker across blue and green wires, music comes out. If I put a speaker across yellow and green, music also comes out. Weird.
I would say that the green wire is a common ground. Check it with an ohmmeter.