I don´t have a wiring diagram for the post 90 models, the connector used to be, on the drivers side of the gas tank, front end, up a ways (two wire connector, small gauge wire). But it could have been incorperated with the fuel pump harness on the injected models.
Said to be a connector, between the dash and the left rear taillight, that I never did find (somewhere under the carpet or kick panels). If you can figure out which wires to test, I´d do a voltage test, near the gas tank, on the colored wire to the sender, then continuity test from the black wire to ground. Should be very little voltage (amperage), need a good contact and ground to measure. Figure out if the problem, is before the tank or in the tank or a ground.
If you can´t find the wire color, a place to look, would be on the back of the gauge, should be the same color and stripe, running all the way back to the sender in the tank (but this is sometimes not so :x ) Usually have to follow the brass circuit board trail, back to the conector to get the wire color. Most of the gauges, I have seen, had three contact points, power, to sender, ground.
On the older models the nuts holding the gauge in, were brass, while the circuit board was copper, oxidation would grow between the nut and the circuit board, causing the gauge to go only part way down. But this was usually a gradual thing.
Wish I could be more helpfull, took me days, to figure out what was wrong and fix my gas gauge.