there are 2 different kinds of accy power in the car... one is with the key rotated back, being in the accy pos..
the 2nd one is on only when the few is rotated forward, like when the car is running.
the 1st one to power my Siruis radio, and the 2nd one for my subs... so that way, if i'm just relaxing somewhere waiting for someone, I can still listen to the raido w/o the subs drinking the amperage from my batt.
Just grab a multimeter, you are looking for 12vdc. If I was home, I would pull out my deck and snap pics and gladly provide you with more info.