farnoush

I have a few questions about wiring the head unit. The first thing i really need to know is which wire is constant power and which is the switched power source? Im looking in my haynes manual at the wiring diagram and it looks like theres only one power wire. ive tried the test light and the only wire i could get it to light off of was lit all the time even when the ignition key was turned to off. Im real confused here and any help would be greatly appreciated. i can get pics of anything if needed.

Sam