Window Defogger Grid Lines Test

GRID LINES
The horizontal grid lines and vertical bus bar lines printed and fired on the inside surface of rear window glass comprise an electrical parallel circuit. The electrically conductive lines are composed of a silver ceramic material which when fired on glass becomes bonded to the glass and is highly resistant to abrasion. It is possible however, that a break may occur in an individual grid line resulting in no current flow through the line. To detect breaks in grid lines the following procedure is required:
1. Turn ignition ON and turn control switch to ON. The LED should come ON.
2. Using a DC voltmeter with 0 - 15 volt range, contact terminal (B) with the negative lead of the voltmeter. With the positive lead of the voltmeter, contact terminal (A). The voltmeter should read 10 - 14 volts. A lower voltage reading indicates a poor connection in the feed or the ground circuit.
3. With the negative lead of the voltmeter, contact a good body ground point. The voltage reading should not change.
4. Connect the negative lead of the voltmeter to terminal (B) and touch each grid line at Mid-Point with the positive lead. A reading of:
- Approximately 6 volts indicates the line is OK.
- 0 volts indicates a break in line between Mid-Point (C) and terminal (A).
- 10 - 14 volts indicates a break between Mid-Point (C) and terminal (B).

Move the lead toward the break and voltage will change as soon as the break is crossed.