- Start the engine.
 
- Activate the rear window defogger system.
 
- Connect a test lamp to a good ground.
 
Important: The test lamp brilliance will decrease proportionately to the increased  resistance
in the grid line as the probe is moved from the battery positive     bus wire to the
ground bus wire. The test lamp brilliance may vary from   one   window to another.
- Move the test lamp probe from zone 5 to zone 1 along each grid line.
 
| •  | If the test lamp goes  out, test the grid
line in at least 2 places (1,3) to eliminate  the  possibility  of bridging  the open
(2) in the grid line. | 
 
- Once the open (2) is located, repair the grid line. Refer to 
Grid Line Repair 
 .