When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Most likley a stuck sender, but the wiring also suffers from chafing and corrosion. It's under the rear seat, so look there first.
If the wiring is OK, have the sender out and move it, watch the gauge.
Then it might be a new gauge.......
what he said lol
if you get to the tank unit under the back seat just unplug it leave the ignition on and give it 5mins the gauge should drop to empty, if it does the wiring and dash are ok meaning the sender in the tank is either stuck or faulty