Check the fuses. Check for ignition power and ground to the PC board and through the spring clip connections that connect the PC board to the voltmeter pins. Oxidation of PC board connections and loss of spring tension on gauge pins are common problems. If the PC board is tarnished, gently polish the copper foil with a soft rubber eraser or crocus cloth. Be careful not to peel the foil loose from its plastic backing. If you confirm ignition power and ground at the voltmeter pins, the voltmeter is faulty.