The gauge and the sending unit should both be 30 Ohms for your year. Can I assume that the resistor is between the 12 volt source and the gauge? Does the gauge go to full when you disconnect the wire to the sending unit? The system is really simple: You only need six to eight volts to the gauge, ground to the case of the gauge, continuity(a wire) from the gauge to the sending unit and a good ground to the body of the sending unit; all of which are easily checked with a multimeter.