That link is certainly informative,.... but the one theing it assumes is there is a big problem... as did I when I had this exact same problem...
The temp gauge was sky high... i didn't have a clue so i called a mate... he said uh oh ... your thermostat is blocked or dead... remove and check it ... so i, being the obedient idiot that i am did this... guess what it tested fine in my kettle and now all my coffee tastes of CJ blood - [but thats good]... then i replaced it... then he said uh oh... that means it might be your water pump could be buggered ... but i dont know - good luck - bye....!
I shook my fist...
I called a jeep mechanic... he said "seen it a 1,000 times"... and is it both fuel and temp or just temp ? I said ahhhh haaa he knows something... just temp i said... he said remove the temp push on connector at the back of the gauge... its 5 cm's up from the bottom of the dash... wait and then turn on the ingition... then replace it.
I did.... it reset the gauge.... and the problem was fixed.
All it was is the contact between the connector and my gauge post was not perfect. Don't go all crazy with volt meters and screwdrivers before you do that... and if its both gauges then remove both wires... but the are in serial so the temp removal will effect the fuel reading as well.
Experience is the best way to learn - and always ask more than one mate before removing a thermostat or anything else for that matter.