How to Troubleshoot a Temperature Needle Gauge That Will Not Work

Trace the tube or wires from the back of the display dial to the sending unit. For some applications, such as an automobile dashboard or kitchen stove, the unit may need to be dissembled with a screwdriver to access the gauge.

Disconnect the tube from the sending unit with a wrench. On electrical gauges with wires, the wires will be attached with metal clips or small ring terminals attached with screws or nuts. Pull the electrical leads with clips off the contact terminals with your fingers. Disconnect ring terminals wires with a small screwdriver or wrench.

Apply heat with a match or lighter to the tube where the tube was disconnected from the sending unit while watching the needle on the dial. Needle movement indicates the tube and gauge dial are working properly, which, by process of elimination, indicates a faulty sending unit that requires replacing.

Check gauges with wire connections. Set a multimeter to the "Ohm" or "1X" setting. Touch one of the meter's probes to either of the disconnected leads and the meter's other probe to the other disconnected lead. Any reading on the meter indicates the wire and gauge dial have continuity and are functioning normally, indicating the sending unit is faulty.

Continue testing if there is no reading on the needle gauge dial. Disconnect the tube from the back of the gauge dial with a wrench and disconnect wires with a screwdriver or wrench or by pulling the clips with your fingers.

Retest the tube. Apply heat to the end of the tube that was disconnected from the sending unit while watching the button on the end of the tube that was disconnected from the gauge dial. If the button protrudes from the tube as heat is applied, the tube is functioning properly, indicating a faulty gauge dial. If the button fails to extend, the tube is faulty.

Test the individual wires on electric gauges. With the Multimeter set to the ohm or 1X setting, touch one of the meter's probes to the end of either of the two wires. Touch the meter's other probe to the opposite end of the same wire. Any reading on the meter indicates the wire has continuity and is functioning normally. Repeat the procedure for the other wire. No reading indicates a short, or break, in the wire, requiring the wire be replaced. If both wires show continuity, the gauge dial is faulty.

Replace the defective part and test the gauge. If the gauge does not function properly, recheck the connections.