There's a wire running down the rear inner wing on the left hand side as you sit in the seat. There's a connector halfway up it and it occasionally comes apart if youve had the seats out or loads of crap rolling around in the back. Worth checking first.

The supply to the tank sender is down the left hand side inner wing , there is a bullet connector for the flying lead that goes to the tank. if you split this and then use a piece of cable that is bare at both ends and use this to short the Female connector the needle on the gauge should jump to life. If not the gauge is dead, 0.1% likely. This lead when checked with the multimeter has about 8v engine off and about 11v when engine running- the gauge is a resistor and so you will never see 12v up stream of the gauge. No V means there is a break in the loom probably on the bulkhead.

if alls well its drop the tank and run a good earth from the tag if its still there or from a ring teminal under any of the screws you can get out cover everything in copper grease for re assembly.
Check the operation of the sender by contacting your meter between the male bullet and your earth and tip the tank if the resistance changes all is well- sometimes the wiper part of the sender wears and snags the resistance winding, sometimes the copper conducting strap breaks with fatigue.

sean
assuming its not the fuse and everything else is working