Hi,

I can feel for your pain in the back while trying to hover your arms up against the rear window and over the package tray.
Your knees get a break from say “a hard floor” but balancing your torso gets to our old backs pretty fast!

I have one defroster not working all the way across but a few grids do heat up.
A previous owners dogs backside rubbed the grid lines down or faint in several places.
I have planned on using Circuit Board Trace fixer many years ago, but those are narrow or fine lines to do that too! It’s a two part conductive epoxy so it’s not exactly resistive.
I figure lots of taping is a big job in its self. So likewise that rear window still waits!


Now, I have a rear window in a 1986 wagon window that has failed to draw current.
I suspect the TABS have failed as they look whitish on the edges from corrosion.
I can hook a battery directly to those tabs or their wires and I get about one ampere of current draw.
It should draw 5.75 amperes.
I know this, because I have a complete spare tailgate “stashed” away. I tested it by the method above.
It takes a several minutes to get the glass warm to the touch, so I know where the current or wattage is getting used up.

Trying to use a digital continuity tester with sound, will get you into trouble when troubleshooting.
Some units will not sound off if the resistance is too high.
The grid creates resistance and that causes voltage drops and to add insult to injury these resistances are in parallel circuitry.
An ohmmeter gets to rambling down too many paths let alone a bad contact point.
The film traces are made with metal oxides coating.
I suspect, don’t know for sure but it’s like audio/video cassette tapes, without the polyester film base as the carrier. The glass is the substrate here like fiberglass is to a PCB.
The stuff is like a house paint that uses a base color oxide with various resins qualities.
The secret is in the resin molecules absorbing or holding the very fine oxides tightly together for continuity.

My problem with the wagon heater is it somehow messes up the consoles electronic switch.
I even get a back feed to an instrument cluster light.
The light and a ten minute timer comes on every time I use the brakes, so I disconnected the grid.

So far I have been figuring things out wrong with lots of half conclusions too!
I’m not the smartest Cabbage-head in the field of electronics either!
Lots of Brussels sprouts leaves put in salad for dinner probably affects my thinking! (:)
I don’t spend the effort in electronics, like she does to make some killer salads!
She just says.”Your not dead yet!”

The third brake light gives the electronic switch power or a grounding path for the switching circuit.
With my Thinking(?) working(?) as if it’s a lack of a good ground though the hinges?
I rewired the whole tailgate and modified the hinge plates for more room for the wiring and a braided grounding cable.
It’s still had to disconnect it until I can try to repair those tabs!
The electronic relay must need a certain amount conductivity or resistance? Puzzling for sure!
I might give up having that timing switch as I don’t used rear defoggers much!
I still have older cars too, I never had a issue with those!

I found this site, that may be the one you found, about repairing these grids. I see they sell a product thats almost uses the same principle of a trace repair epoxy and by the way, just as expensive.

https://frostfighter.com/defroster-repair-tab-bonding-kit-2000.htm

Check it out.
There must be a reason why silver over solder being used now since they made our units.
Ultimately, I think, its the moisture that finally wins!
I might try desoldering them and use some Calgon Heat trap paste used when doing pipe soldering.

Let us know how the work transpires!

Phil