i have a problem with my gas gauge, it wnt read the gas it doesnt move at all

Check and test the fuel sending unit -start here

I dnt think the sending unit is the problem because i connected my old gauge n it was working fine. When i installed the gauge cluster with the tach i didnt disconnect the battery n i still hvnt tried disconnecting n connecting it again

If it works with the old gauge then there's no problem -I don't think the fuel level is monitored by the computer is this what you're implying-disconnect/connect has nothing to do with the fuel level-

Here's the catch:i disconnected the gauge and reconnected it, the needle moved to the middle( im guessing that was how much gas i actually) but later on went back up and does not move now

If I were you best check the fuel sending float resistance/s in the fuel tank-

From wat i can infer. The gauge might be defective. The plug that is on the side where the gas gauge is, broken this could also affect right

Try correcting the wire problem and see if it'll work-could be the gauge itself as you suspected-