one day i was driving down the street and the needle started to jump up and down and i thought it wasn't a big deal so i kept on driving and then it just sunk to the bottom then my check engine light went on and then i checked it and it said i needed to get a new speed sensor so i got one and installed it and still the tach still doesn't work

 

What's the specs on yer T-100? Year, engine, transmission, etc...

Is this the stock tachometer or an aftermarket one? Are you the original owner? Has this T-100 been modified? Did you check the wiring? Are you sure the tach still works? Did you test the signal from the ECU?