volume wont vary, backlight half lit

I installed a pioneer head unit (deh-mp3900) in my 93 regal. I used an existing gm adapter i used w/my kenwood and the pioneer harness included. I had a kenwood deck in before with no problem. I can play cds, listen to the radio use most of the functions on the unit. However, the volume knob wont work, its up way loud, and the backlighting is only working on the left side. I also noticed that it wont turn on in the ignition "on" position.   I hear it working inside the unit, but it wont turn on in that position

ok update.. I plugged the light back in for the glove box and it now works in the on position. I dont believe my car has acc, but tell me if im wrong.   I can vary the volume w/ the remote i found, but still not on the head unit. The lights still arent working, I think I may have a bad faceplate but still unsure.

souds like you have a bad unit.

yep. you nailed it. I went and exchanged it and it worked fine.