Component Tests and General Diagnostics

Glass, Frames and Mechanisms

Component Test

Grid Wire Test

1. Using a bright lamp inside the vehicle, inspect the wire grid from the outside. A broken grid wire will appear as a brown spot.

2. Run the engine at idle. Set the rear window defrost switch to ON. The indicator light should come on.

3. Working inside the vehicle with a voltmeter, contact the broad, red-brown stripes of the back glass window positive lead to battery side and negative lead to ground side. The meter should read 10-13 volts. A lower voltage reading indicates a loose ground connection.

4. Contact a good ground point with the negative lead of the meter. The voltage reading should not change. A voltage reading of less than 10 volts indicates a loose ground connection.

5. With the negative lead of the meter grounded, touch each grid line of the rear window defrost glass at its midpoint with the positive lead. A reading of approximately 6 volts indicates that the line is good. A reading of 0 volt indicates that the line is broken between the midpoint and the B+ side of the grid line. A reading of 12 volts indicates that the circuit is broken between the midpoint of the grid line and ground.

6. Pinpointing the exact position of the break can be accomplished (if the voltmeter reads 0 volt when the midpoint of the grid line is touched with the positive lead of the voltmeter) by moving the positive lead of the voltmeter toward the B+ side of the grid line and touching the grid line until the voltmeter reads 12 volts. If the voltmeter reads 12 volts when the midpoint of the grid line is touched with the positive lead of the voltmeter, simply move the positive lead of the voltmeter toward the ground connection of the grid line and touch the grid line until the voltmeter reads 0 volt.