Using a strong lamp inside the vehicle, visually inspect the wire grid from
the outside. A broken grid wire will appear as a brown spot.
Run the engine at idle. Set the control switch to ON. The indicator should
come on.
Working inside the vehicle with a 12 volt DC voltmeter such as Rotunda
Digital Volt-Ohmmeter 007-00001 or equivalent, contact the broad red-brown
strips on the rear 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 wire (pigtail) connection at the ground attaching
screw.
Contact a good ground point with the negative lead of the meter. The
voltage reading should not change.
With the negative lead of the meter grounded, touch each grid line of the
heated rear window at its midpoint with the positive lead. A reading of
approximately 6 volts indicates that the line is good. A reading of 0 volts
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.