Automotive troubleshooting gm
1999 Buick park avenue gauges go crazy
Check for loose wiring, grounds, or connections at the gauge panel connector. The copper foil wiring has a habit of cracking and failure at this critical connection point.
This could be because the vehicle has a fault in the fuel gauge/fuel sending unit circuit. You need to check the fuses and the wiring system from the fuse box to the fuel gauge. You may take it to a professional mechanic for diagnosis and repair.