I usually wire everything through my ignition wires which are easy to get to right under the dash. But if you dont know what your looking for...a lot of people like to run the wires over to the fuse box in the glove box. I would start with your fuses in your glove box, check them and make sure none are blown. Your gauge problem may be as simple as that. For the overlay, though, the other half of it is still wired in somewhere and you'll need to look for the other half of the connector. Somewhere under your dash. You will need to remove the "knee basher" (remove the two screws and pull it off) to get a better look.
