Rear upper defroster fix

[Jimbojones]

So I’m just writing this up for posterity. I had always been annoyed by the upper grid heater not working, because my rear dash cam is mounted center up under the third brake light. On chilly mornings it would never see anything. I had assumed at first it was whoever installed the window tint broke a window trace. But in other 11-13 Caprice’s I’ve seen since, it didn’t work in those either. I don’t know if this applies to 14-17 cars or not. You’ll have to check if you have a WN.

As I was removing some very poor quality and far too dark tint from my rear window, I pulled the trim panels for access, and found the upper grid was never even connected to begin with. Probably a cost cutting effort by GM for the Police spec cars.

I found these Dorman 926-850 defroster tabs and this Permatex 21351 conductive adhesive at Advance Auto, but Amazon also sells them. The Dorman tabs have four little bumps on their bases and the Permatex recommends a completely flat tab base to adhere properly. So I sanded them both flat. After attaching the tabs on both unpopulated pads with the adhesive, follow the Permatex instructions to the letter or it will not bond, I waited the required 24H for the cure time. Both tabs I affixed in the center of the pad provisions on the window.

In the meantime I made some patch cables. I first tested with a multimeter which wire was 12v supply and it ended up being the purple wire on the passenger side. I used a male spade terminal, to interface with the factory ground on the drivers side, solder butt connectors, 14ga wire, and three female spade terminals to attach to the window tabs. For the passengers side I made a similar patch cable for the 12v supply.

All in all it’s actually a very easy fix, that just so happens to take a full 24h. I hope this helps anyone in the future wondering about their Caprice defroster grid.

[Mooseman]

Interesting. Maybe not a cost cutting thing but could have been necessary to prevent interference with fixed mounted radar units. I remember Fords had issues with the electric windshields.

[Jimbojones]

Oh I never thought of that. Thats highly probable.

[s/c'd cav]

one of the grids is supposed to be a antenna

[Jimbojones]

I thought it could be an antenna too. My 78 Impala had the antenna in the windshield. But nothing was hooked to it, and my radio works just fine. Plus there’s the stubby antenna on the rear roof.

[s/c'd cav]

I thought it could be an antenna too. My 78 Impala had the antenna in the windshield. But nothing was hooked to it, and my radio works just fine. Plus there’s the stubby antenna on the rear roof.

i dont know if its a left over thing from AU , or if it was something done for police use , but police use is something i know it was used for

[elc32955]

Very interesting, thanks for the write-up & the pics! I ran a 2011 9C3 for 4 years and for the life of me I can't remember if the top grid ever worked or not! Only reason I could surmise they'd leave it not functional is perhaps when the upper grid was energized it interfered with reception via the on-glass antenna. I've seen weirder things happen, just a guess on my part.

Eric

[Mooseman]

I looked at mine and there are vertical lines between those top grids. Wouldn't that affect operation and amp draw? It doesn't look to me to be for defrosting but as an antenna. As mentioned, it could be an Aussie thing for some special radio frequency or cellular?