When I hit the switch on the dash to turn on my rear window defroster on my 88 IROC the light comes on and then goes off within 20 seconds. When I hit the switch again it either doesn't go on at all or it only stays lit for like a 1-5 seconds depending on how many times I try to turn it on.

Is the length of time a rear window defroster stays on controlled by the rear window defroster switch on the dash or something else like a relay or other electrical component in the circuit?

Do tell. It's starting to get cold up here in Idaho.

 

Bump.

The manual says that after the defogger has operated a short time, the system will automatically shut off. If further defrosting/defogging is desired, simply activate the switch again. I'm not sure what "a short time" means, however.

JamesC

 

The timer relay is in the button. Bad wires, or a bad connection might also play a part in how long the relay allows the system to work. In most cases, replacing the button would correct this problem. Take a few minutes to check and clean the connections as well !

The defroster in my 95Z works exactly as you described - its a common problem in the 4th gen cars - but the ones in all my Third Gen cars work about 4-5 times longer before shutting off.

 

Had that exact same problem a few years ago, just replaced the switch assembly and everything worked as it should.

 

For my car, it's from my driveway to my exit off the interstate. Around 6 minutes or so.