Hey everyone..

I know this kind of has been hashed-over before but I need to know if anyone has had (or has heard of) a real solution to the issue of the rear defroster circuit wire melting at the Right Junction Block. I've read over the forum and some folks have been lucky to just put in a new circuit breaker for the rear defroster and others have bypassed the junction block altogether and added an external circuit breaker.

My dark green wire (at the Right Junction Block) that feeds the rear radio antenna module/defroster grid has melted the wire so badly it's black from the junction block and about an inch up the harness. Also, the tab that the wire attaches to in the junction block has issues too. You can see it's been heated-up and has melted some of the plastic there but the metal tab looks solid and isn't loose (yet).


The first problem I see is that when I try to split the junction box to see the circuitry/wiring inside to see what's melted I can't. There are tabs around the junction box and on Fords I have worked on you can split the box to see the inside but on this Chevy one it fights it. Has anyone split one of these open?

I'd be more than happy to cut the in and out wires for the defroster at the junction box and add an external 30 amp circuit breaker but it looks to not be as simple as that. The red 60 amp feed wire enters the junction box and it feeds the rear defog relay, the heated mirrors, (not even sure I have those), and the radio. Plus the other half of the rear defog relay connects to the HVAC control (for what I'm thinking is the actual rear defroster switch and the timer for what turns the defroster off after 10-15 or whatever it is.)

So anyone have any ideas? I was thinking of checking the local junkyards to see if they had a Right Junction Block that wasn't melted or thought of seeing what a new one cost from GM but my worry is that unless GM redesigned the wiring and/or the junction block, it would seem as if it would eventually just melt again. I could definitely smell something burning as I was troubleshooting this today because as I would jiggle the junction box my voltmeter would go all over the place checking for power at the rear window defroster.

I think I'll call Chevy tech support tomorrow to see if they have any fixes/updated parts too.

DH

 

$184 for the right junction box from GM....

 

Hey guys,

Got the rear defroster up and running finally! It ended up having 2 seperate issues. Calling Chevy tech support proved futile as they didn't really have an updated right junction box so basically you could spend $230 for a new junction box then you theoretically could have the wiring/pins/box melt all over for you again down the road. I need a safe, consistent rear defroster living in Michigan so here is what I found and how I fixed it:

1. The green wire running from the right-side junction box to the back of the car (feeds the defroster/antenna module) was burned at the right junction box (including the slot for the wire in the fuse box) about 1.5 inches up the harness. Cut the burned wire off and added a pin (bought at Oreillys) somewhat similar to the factory size pin.

2. Removed the factory circuit breaker (2 pin metal-style) for the defogger circuit from the BACK of the right junction box (need to pull glovebox out, disconnect both wire harnesses from the junction box, remove junction box to gain access to defogger relay, etc.) Both the the power seat and defogger circuit breakers (identical) are on the BACK of this junction box. By the way WONDERFUL design GM to put people through all this work when in your infinite wisdom you COULD have made two more spots on the FRONT of this fuse box for both the circuit breaker AND relay for accesibility!!!!! I've NEVER heard of having to ENITRELY REMOVE a fuse box to access relays/circuit breakers!!!

3. Also removed 4 pin rear-defog relay from right junction box. (Warning!!! When you do this so that you may re-wire everything safely for the defogger circuit externally (seperate) from the burned junction box, you will affect your heated mirrors, (if equipped), heated seats, (if equipped), and also your factory radio. When you bypass the right junction block you cut the feed for the above-mentioned items. A 15 amp radio fuse(fed internally in the junction box) also loses power too from this "fix." When that fuse is bypassed you lose a power feed to the radio and to the radio amp. You will need to find those wires and supply a "hot at all times" power feed (15 amp fused) for the radio to work. Also, when you hit your rear defrost button your heated mirrors and heated seats kick-in as well. Once bypassed you will lose these items as well. My car was not equipped with them so I didn't worry about it.

4. Once your defogger circuit breaker and relay are unplugged you need to find the 4 wires (1 green defogger feed wire and 3 other wires) associated with the defogger circuit so you can get them out of the right junction box so you can bypass the junction box. At this point there is enough wiring (if you unwrap the electrical tape from the big wire harness) to take the 4 wires and wire-up your external circuit breaker and relay so that you retain the factory "protections" for this high amperage circuit.

Once all the bypassing/new wiring was done I had 12 solid volts at the rear defroster/antenna module (where before the voltage would jump all over the place when wiggling the right junction box due to the burned-out wiring/box.) I then turned on my rear defroster and the defroster still didn't work! I checked and I had 12 volts going into the rear defroster/antenna module and no voltage coming out to feed the defroster grid. I went to Amazon and got an A/C Delco module for $34 shipped. I installed it and finally we had some rear defroster action!!

One last weird thing is that the rear defroster grid has a left, right, and a middle section. The first few times I turned the grid on the passenger-side portion would defrost first, then the driver's side, then the middle! Now it's been about a week and they all seem to defrost at the same time.

Well, I hope this may help someone that has rear defroster issues down the road. Now I'm off this weekend to fix a driver's side temp door actuator that may need a driver's side temp door replaced. (Have to pull the dash and not watch any football this weekend!)

Good luck!!

 

Sweet! It sucks that nobody here could help you, but at least it's here for a future reference. Thanks!