Hal,
Since I have this problem, too, possibly the same 3 gridlines, I looked it up in the service manual. Surprisingly there is a detailed writeup. Here is the most important information from my (1995) manual, good luck!
Information from the factory service manual:
The grid lines consist of two layers. The outer layer is brown, the inner layer silver.
TESTING:
- Using a bright lamp inside the vehicle, visually inspect the wire grid from the outside. A broken grid wire will appear as a brown spot.
- Run engine at idle, turn on rear defroster.
- Working inside the vehicle with a voltmeter, 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 reading indicates a loose defroster ground wire - check the
defroster ground wire attaching screw.
- Contact a known ground point with the negative lead, the voltage reading should not change.
- With the negative lead of the meter grounded, touch each grid line at its midpoint with the positive lead. A reading of ~6V indicates the line is good. A reading of zero V indicates that the line is broken between the midpoint and the B+ side of the grid line. A reading
of 12 V indicates that the circuit is broken between the midpoint of the grid line and ground.
REPAIR:
Any break in the grid longer than 25m / 1 in. cannot be repaired.
If the brown layer is damaged or missing, apply brown lacquer touch-up paint on the window glass prior to applying the Rear Window Defroster Repair (D8AZ-19562-AA).
-The vehicle should be warmed to 60 deg F or above.
- Clean the repair area with window cleaner.
- Mask off the area above and below the grid line.
- If brown layer is broken/missing, apply 2 coats touch-up paint. Extend 1/4" past both ends of the break.
- Apply 3 coats of grid repair, Extend 1/4" past both ends of the break.
- Allow 5 minutes to dry before removing mask.
- Defroster can be energized after 3 to 5 minutes.
