1981 Rear Defog stopped working

[1981]

My rear defog stopped working, I searched the forum and the word defog doesn't pop up anything. I guess this is a first for this topic?

Well, needed my windows defogged in the rear so I hit the switch and nothing happened, the light didn't come on and the rear window didn't defog. Got home and decided to finally start making sure my electrical under the center console is put back in order. Over the years no-one who stuck their hands under there knew what they were doing. Gonna be putting in a KENWOOD-X569 MP3 player within the next few weeks, and man do I have my work cut out for me, litterally, the previous owners really did cut all of the work (the wires I need for my radio) out.

Gonna me to ing

Back to the topic,
I shot power to the switch connector and it looks good, I do not know what I should be getting, but the ground is the ground and I get 11 VDC between the two terminals. There are four terminals.

I shoot the switch itself and in the on position I get NO continuity between any terminals.

I figure the switch is bad, so I pull the switch and the box connected to it. I disconnect the switch from the box and the swith works good. Nothing mechanically wrong with it.

I pull the circuit board out of the box and there is a fried resistor right next to the three (3) terminals the mechanical defog switch makes contact with. This resistor is also right above the contact coil. Well I have found an obvious bad component, but after searching all of the major parts places, I can not find this box. Anyone know who sells this part? It is the box connected to the defog switch. or is this part of the defog switch?

I am hoping the part was just so old it fried under normal conditions. I really do not want to start hunting a shorted wire down. Anyone else have problems with their rear defogger?

1981

 

[vettenick]

Sorry to inform you, but that box is the relay/timer control for the defogger. It's all one part. I would check Eckler's or Zip products. If the relay is bad, you won't get power to the rear window.

 

[1981]

So this is the infamous relay/timer for the defroster?

Well at least I know what part to start looking for. Thanks a lot for the guidance. I am not sure if the relay is bad or not, the resistor that is fried is for the small light bulb inside that lights up the switch when the defroster is on, which is when the relay is closed. I just need to buy a new relay/timer.

1981

 

[clar2001]

I have a 75 does the rear defoger use heat to work ?

 

[vettenick]

1981- that timer/relay is actually part of the defogger switch.

 

[vettenick]

Clar2001- 1975 just uses a blower motor. There's nothing to indicate that you should expect hot air from this blower.

 

[clar2001]

Thank you

 

[vettenick]

You got it!

 

[theo]

Why not try putting another resistor in? I don't know the correct size, and I appreciate any markings may have burned off your one, but have a look at http://iotech.no/corvette/index.htm the 1980 vette site, and go to the technical articles. There's some really good stuff here, inlcuding info on doing work on the rear defog relay.

Don't sell your house to buy a new relay from one of the restoration places just yet! They sell great stuff, but they can be bloody expensive..!