1991 Camaro, rear defrost does not work all of a sudden. I can turn the switch on, and it clicks, lights up, and stays on for 10 minutes as designed, but does NOT defrost the rear window at all.

I have gone through and checked voltages using the following guide: https://www.thirdgen.org/forums/elec...-how-test.html

All voltages read as they should, EXCEPT 5-7 on the second part of the list (lift support wires and actual defrost grid on the window), which all read 0.4V regardless of the position of the switch. Hatch lift supports have been on there since 2017, and I have never had a problem with this set. All wires going to them have a good connection as well.

Any ideas? Could the switch still be bad, even though it shows correct voltage at all wires going into it?

 

I had the same issue on my Firebird and it turned out to be pitted contacts at the hatch connection point. I cleaned upper and lower contacts and all was OK after that.
These pictures show pitted contacts.





Also make sure the Stacon connector hasn't pulled off of the gas spring on either side.

 

I always thought those contact points were for the third brake light?

 

Pretty sure they are. I don't have contacts like that on either of my '91s.

 

Thanks for keeping me honest guys. You are correct and I should know better than to rely on my memory. Those contacts are for the high mounted stop light.

 

 

Showing 0.4V at both of those points with defroster on and car running.

 

On my '83, the passenger side is a ground point, short lead of wire to body ground screw (interior is out right now so I verified). Check to see if there is continuity to body at that point with the meter. Then check to see if there is voltage from the driver's side to body (the strut mount bolts can your test points as they screw into the body).

 

Well, forget everything I said. I checked the purple white wire from the kick panel all the way back to the LR defrost lead, showed 0 volts, so I checked the switch AGAIN, and now the purple/white wire is showing 0V at the switch when the switch is on. So I guess it's the switch.

 

You may well be right, but consider these possibilities as well.
The purple and white wire at the defogger control switch feeds the on indicator pilot light at the switch as well as the defogger feed. That purple and white wire comes from the solid state timer.
Check the Power/ACC circuit breaker and gages fuse are Ok and the solid state timer is turning on if the breaker/fuse are good. If the breaker/fuse and/or timer is faulty, your switch may be OK. The light blue wire at the defogger control switch starts the timer so check it to make sure it is supplying 12 volts to the timer when the switch is turned on. That light blue wires voltage, is a better indicator for whether the switch is faulty.



Please keep in mind this drawing is from the 1988 service manual as I don't have a 1991 manual.

 

Firebird and Camaro defrosters are different. Firebird has a separate relay behind the passenger's side of the dashboard; on Camaros, the relay is built into the switch, so there's no Light Blue wire. Power/ACC circuit is good, as the power locks work fine. According to the flow chart on my '92 manual, it's the switch, so I'm going to try that next.

Thanks!

 

Sounds good. It really helps to have the right manual.
When I joined this group about a year ago I was under the impression that all 3rd gen vehicles were built mostly the same, but they aren't. They can be different from year to year, model to model, and now it seems Camaro to Pontiac are different as well. Thanks to the group I am continually learning.
Thanks.

 

There’s a relay too.

 

Only on Firebirds for some reason. Relay is built into the switch on Camaros.