just got my first 85 12a a couple months ago now its on jack stands,so i had to put a new fuel level dending unit but the gauge still doesnt work it moves when u touch the yellow wire with a test light but other then that it stays on empty where is the relay for this i tried looking at a wiring diagram but it wont say where the relay is located...

 

There is no relay. You have the sending unit and then you have the gauge. In my signature is the link to the FSM. Download a copy and you will find the test procedure to test the gauge and sending unit in there.