You can buy an adapter harness that plugs into the existing wiring. Hacking up the original wiring will run you into trouble if you don't know that you are looking at. When you plug in the after market harness its all color coordinated to almost any after market radio deck. Adapter harnesses are sold at almost any Wall Mart, Best Buy, Future shop or audio/electronic store there is. They are about 5-8$ on Amazon or Ebay.
96 300ci M5OD 2wd Reg Cab Long Bed 3.31 LS Gears and 8-Track player
A question that sometimes drives me hazy: am I or are the others crazy?