you can test the sender with a multimeter set on ohms. 0 is empty, 90 is full. There is a connector at the back of the tank, it's a pink wire. Make sure the ground wire is getting a good ground. You can test the sender with the wire that comes from the sender. It's best if you have an empty gas tank with gas in a container so you'll know how much gas you have in the tank when you put some in to check the ohm reading. If that reading is good then attach the wires and do another ohm reading check on the pink wire at the left side of the fuse box. If that reading is consistent with the reading you had at the tank then you'll need the check the wiring to the gauge and then the gauge itself.