To locate inoperative grid lines, start engine and turn on the rear window defogger system. Ground test lamp lead and lightly touch the other probe to each grid line. Refer to the pattern of test lamp brilliance to be expected with a properly functioning grid. If test lamp bulb shows full brilliance at both ends of grid lines, check for loose ground wire contact to body metal. (1) No bulb Brilliance. (2) One quarter bulb brilliance. (3) One half bulb brilliance. (4) Three quarters bulb brilliance. (5) Full bulb brilliance.

The range of zones may vary slightly from one window to another; however, the bulb brilliance will decrease proportionately to the increased resistance in the grid line as the probe is moved from the left bus bar to the right. All grid lines must be tested in at least two places to eliminate the possibility of bridging a break. For best results, contact each grid line a few millimeters either side of the window centerline. If an abnormal light reading is apparent on a specific grid line, place test lamp probe on that grid at the left bus bar and move probe toward the right bus bar until light goes out. This will indicate a break in the continuity of the grid line. (1) No light. (2) Broken Grid. (3) Full brilliance. (4) Rear window. (5) Feed bus bar. (6) Ground bus bar. (7) No light. (8) Ground bus bar.