vett79

The rear window defogger on my '79 quit working. Fuse is good. The next most likely suspect part is probably the timer/relay. Looks expensive and I've not found it in any of my catalogs. Anyone run into this?

Ingar, Norway

Yes, I had this problem.
It turned out to be a fault in the relay. There are some power transistors in there thet have poor support and they develop cracks in the soldering to the PCB. Resolder solved it.
The same goes for other relays containing electronics, viper and interior light.

figment3

most of the releys are the same trough out the chevy line,all though the problem with nine out of ten rear defogs is a bad ground on the far side of the rear glass. take a test light and ground one lead,then touch the wires of the grid and see if you have power to it.should be strongest in the middle of the glass.no light means no ground.

TFeld78

I have the same problem, but have never checked it out. Have not looked
it up in the manuals, so, where is the relay located? I will also check
out the suggestion of a bad ground. Unfortunately, I have to wait a week
when I get the car back (with a new differential!!).

Paul L

The timer relay is located under the left side of the shifter console.

Ingar, Norway

Ok, then it was moved in 1980. My relay is located in the passenger side compartment.
Btw: I have a mod for extending the "On"-time at my page. (+ all 1980 schematics)

VTHokie77Vette

On my '77 I have the little Rear Defroster switch and it lights up when you click it, but my back window is just plain. Were they all made with a working switch or was the back window replaced???

vett79

Thanks for the suggestions.........I'll try the test and the resolder if necessary. :)

jimm39

You can find the rear window defogger relay on E-Bay for I think around 13.00 america dollars