Between the rear passenger window and the back window is a junction where rear defrost wiring and radio antenna connect. Rear defrost wiring becomes loose and burns this unit out. when looking for replacement at salvage yard everyone of them I found had burned up. Lots of La Sabres w/o working rear defrost. I made solid connections for defroster, and added an antennae, not much point in repeating a system that will fail again.
SOURCE: rear window defroster wont work.
First place to check is under the wide trim piece that runs over the back drivers side door and also runs to the back window. You can pull this away from the body. It just snaps in place and the seatbelt goes through it. Pull it down toward you and you should see a black box fastened to the side of the window pillar. It should have three wire connections. One is the radio antenna, one goes to the window and one comes from the wire harness. Check the two wire connections from the harness and to the window. See if they are loose or in my case the one from the harness was burnt and had melted the black box where the wire went in. I had to replace the the wire connector and the black box ($72.00) and replaced the connector terminals. The replacement connector is available but that little thing is pricey ($32.00). They must be proud of that thing.
Hope this helped.
SOURCE: rear defrost on 1999 buicl park ave
Jeff, If you have already checked the fuses, check the wires attached to the defroster Grid. You may be able to see them inside the rear window. Make sure they are still connected. You might also want to check in the trunk the wires may run into it, and might have peen pulled apart when you put somthing in the trunk. As a last resort take a continuity tester and check the grid itself to make sure it hasn't failed altogether. Un plug the wires b-4 you test it to avoid a false reading.
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