Start the engine and turn on the rear window defogger system in order to locate inoperative grid lines. Ground the test lamp lead and lightly touch the other prod to each grid line.
Refer to the above figure for the pattern of test lamp brilliance to be expected with a properly functioning grid.
Inspect for a loose ground wire contact to the body metal if a test lamp shows full brilliance at both ends.
The range of zones may vary slightly between different windows. The bulb brilliance will decrease proportionately to the increased resistance in the grid line as the prod is moved from the feed bus bar to the ground bus bar.
Test the grid lines in at least 2 places in order to eliminate the possibility of bridging a break. Contact each grid line a few millimeters on either side of the grid line centerline in order to obtain the best results. Perform the following procedure if an abnormal light reading is apparent on a specific grid line.
This procedure will indicate a break in the continuity of the grid line.
Refer to the following figure for the pattern of test lamp brilliance to be expected with broken grid lines.
