88 Ranger audio. HELP!!!

I have put a ton of aftermarket CD players in vehicles, but this one is stumping me. I have it all wired up and secure but only the front speakers are working. Now there was a wire attached to the back of the factory Cassette player...when its grounded where it was on the new deck the speakers cut out completely, but when you leave it loose the speakers work, but the deck doesn't shut down when you turn the ignition off. Can anyone give me a trick or quick fix for these problems? :banghead:

Whoops. Apparently posted this in the wrong place. Well if there are any moderators looking through can you move this thread to the Car Audio section? And as an update it appears that the factory system has an amp that powers only the rear speakers where that red wire grounds to the back post of the factory cassette player. Doesn't explain why the front speakers cut out when it is grounded though.