What is wrong with my electrical?

I have a '99 Chevy Cavalier, and my odometer numbers do not come through correctly sometimes, and has started to get worse. After that, my gas guage has started to act up, I can never tell how much gas is in there because the needle moves around every few minutes. Lastly, my turn signals stopped functioning. I've replaced the bulbs, all internal signal parts, but the light just stays on when I put on a signal. I can wiggle the part it connects to under the dash by my feet and that seems to make it work for a few minutes, but then it'll go out again. Do I have to replace my entire electrical system or is there an easier fix?