In the original wire harness, you have two connectors, a black and a gray. I'm talking about C211, the GRAY one. On pin 6, the red/wht wire, you should have 12V when ign is on or in accy. This goes straight back to fuse 12, a 10 amp fuse. If you don't have voltage at the radio connector, try measuring voltage one either side of the fuse to ground. You should have it (with key on) on both sides of the fuse. Only on one side indicates blown fuse. If you don't have it on either side of the fuse, you have bigger problems, on the path back to the ignition switch.
You should also have 12V on pin 7 of C211, the Pink wire. This is always on, regardless of ignition key, and goes all the way back under the hood to the power dist panel by the battery. There it is protected by a 5 amp fuse. It is to provide power for the radio's memories and clock.
BTW, if you don't have a voltmeter, a simple test light would work for checking these circuits, just to see if you have power or not.
Your aftermarket radio should operate at least, on the power from pin 6.
Good luck.