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

Thanks for your thoughts. Regarding voltage, I did test this morning with the engine running and got a bit over 13 volts which is my battery voltage. It jumps around a little, of course. Regarding continuity of the grid itself, see my response from this morning to Dave Stevens' post. I am still not sure what is going wrong or what to think. Cheers!

Here is a progress report... With regards:

o Connect one of your voltmeter test leads to a good chassis ground (you can use the right side defrost tab if that is convenient).

o With the defrost switch ON, try probing with the needle into the grid near the left (driver side) tab. If you don't see any voltage there (but still do at the tab connector itself) then that tab is your chief suspect.

o If you do see voltage there then try probing into the right side of the grid. If you still see a bit of voltage over there then that confirms (at least some of) the grid is okay and the problem is likely at the right tab.

I managed a good ground in one of the holes in the rear deck where the clip that fastens down the carpet is missing. I was able to confirm this ground with continuity sound to the right side tab on the window.

With engine running and defroster switch on and lit up, I get 13v at the left side tab and, with a sewing needle clipped into an alligator connector, I have probed up/down the majority of the left side strip under the tab getting voltage at pretty much every location. This makes me think the connection between the left tab and the window is ok.

When I look for voltage at the right side strip under the tab, I seem to find nothing. But I do note that in at least a few places more proximate to the left side, I get some voltage response when probing some of the grid wires directly. So I conclude that at least some of the grid wires still have a connection to the left side strip. But this suggests that virtually all of the grid wires are kaput somehow in their attempt to reach all the way across the window.

With regards:

o Try probing into the grid at the right side. If you see a hint of meter action then that suggests the right side tab is okay. Probe over on the left side of the grid and if you still see a bit of continuity then that confirms the grid is okay and it's likely at the left tab.

With engine stopped and defroster switch off and the same ground arrangement as above, I probe for continuity sound up/down the strip under the right side tab I get the sound pretty much every where I probes with the needle. This suggests that the connection between the right tab and the window is ok too. When probing the grid wires themselves proximate to the right side, I find virtually no continuity sound.

So now I am left trying to probe the grid wires themselves. This isn't easy so I first did a close visual inspection of all the wires, all the way across the window. I do NOT see any apparent breaks in the wires of any kind. But I do note that the width of the wires is uneven. Some wires appear to be thicker/wider than others. Some wires appear to be thicker/wider on the either the left or right sides (or both) than in the middle of the window. I am not sure if this is normal/expected or not. But I simply do not see any complete breaks through the wires at all.

I should be clear that when using the needle, I tried very hard to NOT scratch the wires - only to point and press in. And due to the quite thin appearance of the grid wires in some places, my aim may have been less than ideal. But I do think I found enough decent probings to feel that my report above is accurate enough.

Does any of this sound familiar or explicable?

Thanks!

From one Dave to another, I cannot thank you enough for this detailed help. I will be out in the rear seat again (man, as I get older going back there gets ever more difficult) and follow these very reasonable steps. Will report back. Cheers!