93 Taurus GL Wagon, Rear Window Power Problem

I am hoping someone has an idea on this one, because I've exhausted by bag of tricks -

As it has done once before, one of the metal tabs on the rear window glass that provides power to the rear defroster and wiper/washer, broke off. I followed the previous fix I did by again regluing the tab, which is the same fix any Ford dealer would do (I checked). Now I have a very strange problem. I found that the rear wiper would not work. The washer pump to the rear window still worked. When the rear wiper button was depressed, the rear defroster button lights up on the dash and cannot be shut off until the rear wiper button is turned off. When the rear wiper button is turned off, the rear defroster button can be turned on and off and behaves as it should.

I checked all the connectors and wiring on the rear glass, checked the other tabs to make sure there were still connected properly, checked the two wiring harnesses leading to the rear tailgate for chafing/broken wires (behind the plastic shroud at the top of the tailgate). Nothing looks amiss. I also made sure none of the glue had touched the other smaller connector near the one I had glued.

This is where the strangeness starts. With the rear glass locked down in the tailgate, I happened to lift up slightly on it and saw some sparking down where the hooked locking tab in the rear glass locks down into the recepticle for that tab. If you keep the upward pressure on it, the sparking will stop and the rear wiper will work, and the rear defroster button light inside the car will go out as it should. The rear defroster button can be turned on and off and the button will light and go out as it should again.

For the time being, to prevent a spark starting a fire in the back, I put a piece of electric tape on the hook in the locking tab. The sparking stops as the connection is broken with the electrical tape there, the rear defroster can be turned on and off and will light and go out as it should, but the rear wiper won't work, which is what I expected would happen. At least no chance of a spark making the car go up in smoke.

I am puzzled about the sparking in the rear glass latch - why? Does that latch complete a circuit for the wiper or serve as a ground in the circuit? Any ideas on how I can fix this? Could the problem be in the tabs/wiring right near the rear wiper itself? I'm truly at a loss here, so any ideas would be most appreciated.

If I can't solve it myself, then it's just going to stay broken, as my mechanic feels it will take a while to solve, will cost alot in labor hours, might require replacing the window glass itself (big $$$$), and won't be worth the cost in the end. After all, when I was growing up cars didn't have rear defrosters or wipers, and we all seemed to still be able to get from point A to point B just fine.

Other than that this has been a great car for us, very reliable, few problems, and with 107,000+ its now been passed on to the kids and its still showing no sign of being ready for retirement. So if i can, I'd like to solve this one. Thanks all.

recheck the tabs to make absolutly sure u didnt cross the 2 circuits. maby the latch completes the circuit, clean it up scrape or whatever, turn the wiper and defroster off then see if u still get the arcing on the latch. let me know

maspoon, thanks for your reply. Nothing is crossed, the two connectors per side are different sizes to prevent that. I reached the conclusion that the latch must play into the equation, perhaps to prevent operation of the wiper/washer/defroster if the liftgate glass is up. I was able to strategically glue in two pieces of a rubber, which creates just enough upward pressure on the latch to resolve the problem. I checked operation of wiper/washer/defroster during a snow storm yesterday and both are now working. With the rubber in place the arcing has stopped, but I suspect if you go over a big enough bump and really jar the latch, some arcing will occur. I can always add another layer of rubber in if when driving operation becomes intermittent on uneven pavement. I'm guessing that after 12 years of use something has worn down on the latch hook, such that a positive latch connection was not being made for whatever safety mechanism/switch is there to prevent operation when the glass is up. I suppose the safety mechanism/switch might be worn too, or perhaps both items are. I might try and get a new latch hook, since its very easy to replace, should not be too expensive, and might eliminate future problems down the road. Thanks again.

Hmm...wonder if they put some insulation there from the factory that is gone, also did you check the grounds for that part of the circuit to see if one is dead or floating?