My dashboard is not working except the battery needle and the oil needle and my battary light is on?

I have a 2000 gmc sierra 1500 4x4. My dashboard is not working except the battery needle and the oil needle and my battary light is on. Sometimes all of them work but most of the time the lights that come on when you crank the truck blink and all of the needles will flicker! I believe it may have something to do with my radio and my sub speakers! Is it a fuse or lose wiring or what? Dad thinks it could be altenator