On my Amigo, the stock fuel pump wiring comes in under the passenger seat and the stock temp gauge wiring comes in behind the glove box -- these are grounded separately in each subharness (one at the rear crossmember, which is a rust magnet, and the other by the passenger-side hood hinge).

Not sure why you'd lose fuel and temp but not oil, either from signal or from instrument panel power.

Check the connectors behind the gauges, perhaps?

Randii