Help got new cd player and now my speedometer wont work

i have a 1996 monte carlo Ls which came with a stock cd player but wouldn't play burnt cds so i bought a cheap jensen cd player and a wiring harness. But when i was hooking it up i noticed that i had some wires that couldnt go in to the new cd player. So i just left them. When i hooked up everything else and went to work i noticed that my speedometer wasnt working then i started to hit buttons and turned my cdplayer off and the speedometer worked.

Does any one know why this happened?