My gauge is not reading full, ever.

When the car is off and/or battery disconnected, the gauge needle is past empty (gauge is in the 4 gauge center console). When the car is turned on and the tank is completely full, the gauge reads between 1/2 to 3/4 full. I have never run it to empty so I don't know if it would accurately point to empty when it was in fact empty.

I have read about grounding under the center console as a possible cause, bad gauge, bad sender unit, bad grounding at the sender unit. Not sure where to start. I don't really have the means to drop the tank and start troubleshooting there.

I did buy a new gauge on the off chance it's something simple like a bad gauge but I haven't installed it yet.

Any suggestions on where to start troubleshooting?

 

This sounds familiar! Process of elimination, start at the gas gauge. Disconnect the wire that's going back to the sending unit, leave the power wire attached. With the key on, the needle should peg beyond full. Now take a separate wire, connect it to the stud that the sending unit wire was on, and touch the other end to a good ground source. With the key on, the gauge should peg beyond empty. On to step 2 if that checks out.....