Take a look down at the kick panel in front of the drivers door. Behind it is the an electrical box and the gauge is put in with a bullet which taps into one of the connectors. My guess is you just kicked it out... GIVE that thing a wax BTW. It keeps the oxidation away in that cali sun.
PM me if you still have issues with the gauge but 10-1 that should solve it. Never was keen with how they chose to wire it in but I'm also not a fan of cutting and splcing into the wiring harness.
Why on earth did you replace the visor? It should've been perfect. It was never used for 10 years of its life.
For future reference the gauge and its sender are from Summit. Norsdoq brand or something like that.