How to "test" a head unit?

You just need a 12VDC supply and a speaker or two. You have to have the wiring harness to test it though.

So there isn't any way I could just give it temporary power to turn it on? I bought it at a yard sale super cheap from some lady who didn't even know what it was.

if you have a power inverter /jump starter things it's easy

I used that when I sold mine on ebay, hook the two power wires to the red cable, ground the other, hook up one speaker and flip the power switch

like this
http://www.amazon.com/Amico-HW-02-Portable-Starter-Compressor/dp/B00062I2XE

That's real. Shouldn't you be purchasing a car before you get accessories tho?

Yea Black to ground red to power the rest are speaker wires. I'd hook up at least two speakers as some units may blow with just one hooked up. Plug in an ant and you are ready to test. The speaker wires will be solid and stripped, it don't matter how you hook them up for the test just be uniform. (speakers have Pos and Neg) There may be a yellow wire or orange that also goes to a power source (+) for the test. (it normally goes to Batt for memory power.) That should do ya. Just don't short anything out during the test. Tape the + wires on everything. MC