Check the window defogger fuse. If it is blown, replace it and operate the defogger to make sure it is working now.
Open the driver’s door, turn the ignition switch to the “on” position and, as you look at the interior dome light at the ceiling of your vehicle, turn on the defogger switch. If the light stays bright, proceed to Step 3. If the light seems to go almost off, go directly to Step 5.
Start the engine and turn on the defogger switch. Check for incoming voltage on both sides of the connection at the grid of the rear window using a test light. Repair the connection if necessary. If you detect incoming voltage at the connection as you operate the switch, make sure there is current flowing for about 10 minutes. Otherwise, the timer relay is defective and you need to replace it. Turn off the engine.