The rear window heater is a set of horizontal conductors deposited on the inner surface of the rear window.
1. To detect a break in the rear defroster wire, turn on the ignition and the rear defroster switch.
2. Connect one probe of the voltmeter to the mass of the car, and wrap the second probe with foil and move the foil along the heater conductor.
3. Connect a voltmeter lead to the center of each rear defroster wire. If the voltmeter shows a voltage of about 5 V, then the heater conductor is good. If the voltmeter shows a voltage of 0 V or 12 V, then there is a break in the heater conductor.
4. To locate a break in the heater conductor, connect one voltmeter probe to the positive terminal of the heater, and move the second probe along the heater conductor from the negative terminal of the heater. The point at which the voltage indicated by the voltmeter drops from a few volts to zero is the location of the break in the heater conductor.