When I press my rear defrost button in my 87 T/A the indicator light comes on, but it doesn't defrost the rear hatch. After awhile the light will just go out and shut off. Sometimes when I press the botton either on or off I hear a little ping kinda like a spring. Why doesn't this damn thing work. Half the time I can't see out the back.

 

Sounds like the connections in the back on the window itself have broken...Common problem for these cars, check the connections. If they are good, then one of the lines may have been scratched to the point where the connection has been lost. Then there is alway the relay, but most likely a connection though..HTH

Keiran