i have an 88 fc as seen in the sig below. i took out the gauge cluster to change a couple bulbs out and when i put it all back together the speed-o bounces around.. ill be doing 30 and it will be bouncing from 50 to 180. what could cause this?

 

a wirring issue, unless you moved (repositioned) the needle...

 

needle is fine.. i think its the cable but idk

 

lube up the speedo cable or redo putting it in