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Rear Defroster not working

JohnnyC

Well-known member
Joined
Jul 5, 2002
Messages
262
Location
NJ
Corvette
1996 Black Coupe - LT4
I read threw and tried everything from the previous threads and i'm still not getting any voltage back to my rear window defroster struts.

All my refroster lines are intacted and tested with my multimeter by resistance.

I replaced the relay and did not do anything. (1996 relay is to the right of the steering wheel under the dash). I can hear it click on/off when i press the button.

I believe the switch works(?) since the light just above the defroster icon works and the relay clicks.

The connects to the rear struts have been "replaced" since both sides melted a few years ago. I replaced with standard female connector and crimped closed. I could actual solder them, but i dont think this is the problem since it worked well for awhile. What voltage should i get across the rear struts?

I checked the 40 amp RR defrog fuse under the hood. It was ok.

Ground? Well, not sure how to find this or if its the problem?

Any... any... any other ideas? I'm "ok" with electronics, but not super. I have basic multimeter thats about it. This is driving me crazy and with the cold weather now in wonderful NJ, i really could use the rear defroster working.

Thanks,
John
 
Prove wiring is OK first.
Disconnect relay and confirm you actually have 12V supply coming in from defog fuse.
Then jumper the in / out wires at relay and check for voltage at the struts.
If you have power at relay but not at struts them maybe a bad connection in rear loom.

More than likely the defrost light is on the control side of the relay.
Lights up to indicate you have the switch on
NOT that you have power on the "switched" side of the relay
Would not be indicative of power coming out of relay.
 
Thanks for the info. This is killing me because its been bitterly cold and icy almost non stop in NJ. I have been ready to try this for weeks. The weekend is coming up and should be in the 50s. So i'll try to locate the problem.

I have found that my outside mirrors defrost. Does this help diagnose the problem? If those work, does that mean the relay wiring is ok?
 
Power at the relay! Ok. Took out the relay and found ~12 V at the connector. Jumped the in/out (power from battery #30 and to the power to defroster #87). Still nothing at the rear struts.

There is a bundle of wires wrapped up under the rocker panel along the passenger seat, then some wires behind the seat. They all are wrapped in electrical tape. I didnt notice any breaks from the look i took.

Where is the ground for defroster?
 
Think it's behind the "B" pillar cover panel

The ground should be bolted with 1 or 2 other wires with eyelets behind the drivers side interior panel covering the "B" pillar post. I assume you know but I'll mention it any way, the engine must be running before power is supplied to the rear glass grid.
 
The ground should be bolted with 1 or 2 other wires with eyelets behind the drivers side interior panel covering the "B" pillar post. I assume you know but I'll mention it any way, the engine must be running before power is supplied to the rear glass grid.

Yup. Testing the rear defroster with engine running.
 
And so this continues... i checked grounds all looked ok, no corrosion, not loose, etc.

I unwrapped the bundle of wires that run along the passanger side rocker panel. There was about 15-20 wires in there and did not see any broken. I did find a repair on a green wire that my mechanic had done ~1 yrs ago that he said was for the turn signal. He said it had rubbed on a bolt or something and shorted out. There was a little jumper wire in there and looked ok with 2 connectors. I have no problem redoing that.

Anyone know which color wires goes to the rear window defroster in that bundle? There must be a break in wire someplace!!!
 

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