Chevrolet Repair: 97 Chevy Cavalier factory wiring/ speedometer, factory wiring harness, chevy cavalier

Question
I just recently installed a new stereo in my 97 Cavalier and the factory wiring harness had been cut so it took some research but I have all the wires from the stereo going where they should be and have distinguished which wires are speaker wires coming from the car.  The stereo works great but the speedometer is no longer working.  All other gages are working but the speedometer. Now, there is a gray wire that controls the dash lights and I have it connected so that they only come on with the headlights, which is how it is supposed to be... I think.  There are two wires coming from the car that were left over after stereo installation. One of them is a little thicker than all the rest and it is brown.  The other one is the only one with a stripe and it is green and white.  Somehow I think the green and white one is the one that controls the speedometer, but I have no idea what it needs to be connected to in order to make it work.  I have done some trial and error but I don't want to fry anything, if I haven't already.  It sure would be nice to know how fast I'm going again! :)  Please help if you can.

Answer
Hi Mindy... the quickest way to figger this out is to hook up scan tool and drive the car... go to the screen that would show mph and see if it registers...if not i would check the pick up sensor at the trans...if it does check the plug at the dash and see if you have a referance there.if you do, it's the speedo head.. if you don't trace the wire back to the computer for the open. hope this helps