Dash gauges go crazy sometimes

My tachometer stopped working years ago. It would work intermittently. Then the other gauges wouldn't work or would bounce around. The tachometer needle of course broke off when I put it in park. The gauges seem to respond to bumps while driving and hitting on the dash. At times all the gauges work including the tachometer. Sometimes the tachometer will work when running but will show 4,000 rpm's when turned off. I am thinking its the connection since bumps and hitting the dash seem to effect it and sometimes they work. What is my problem?