Is this possible? I don't want to go to all the trouble of having to rewire the harness just and plug it in, and eject the thing. Said deck is a Pioneer DEH-245 from like 1998, by the way.

 

Carefully wire the positive and the dimmer control to the positve terminal on a battery, and the ground to the ground. Make sure while you are hooking this up that the wire harness is not plugged into the stereo untill the connections are made. Just be carefull that's all.

 

Well you could always use a screw driver and rip the whole thing apart to get the CD out. But Cruzin Kaz's idea would work a whole lot better. Just hook the wires up to the battery(+,-,dimmer wire), then connect the harness to the CD player.

 

wire it like this just to power it up temporary...

twist the red and the yellow (battery, ACC) wires together.
this is your 12v input, put a butt splice on it and add a wire.

do the same to the ground wire. if you can find a generic cigarette adapter with two wires on it that you can splice into the 12v and the ground leads on the HU, this would be the safest way, just be sure to put the ground to the ground and pos to pos!

it should light up and spit the CD out. you can do this with most 12vDC power supplies..like if you have an old computer case, you can butcher the 12VDC wires from the power supply and use those, or a portable batterry charger.