Car Stereos: my blazers radio, best bet, common ground

Question
my problem is that im wiring the radio without a harrness wire to wire and there r more wires on the radio then in the truck

Answer
Some factory stereos are wired using a common ground wire, or go to a seperate amplifier located elsewhere.  The best bet is to buy the aftermarket harness for about $10 and use the instructions that come with it.  It probably will loop a couple of wires back into the other holes to make enough connections to match the radio.  Otherwise, you can buy a repair manual for $20 for your model, and it will tell you what each wire is for, and give you the info you need to wire it correctly.  Hope this helps, Scott