The heated rear window in the Mk2 and the other Jaguars of the time is a neat design. There are two layers of glass like a laminated front screen. The heating comes from very fine vertical wires that run up the screen rather than across. They are joined to thin ribbons just inside the edge of the glass. One runs along the top edge of the screen. Two ribbons (or one with a break in the middle) run along the bottom edge, again just inside the glass. Live and ground leads are soldered to the outer ends of the two lower ribbons where they are exposed. Thus, when it's working, current flows up one side of the rear window and down the other.

Amongst my assorted spares, I have a heated rear window. It's preferable to the non-heated one in my car as it doesn't have pock marks caused from careless use of an angle grinder. I've never had great use from heated windows as I keep my cars garaged; however, if something is there, it may as well work. I recently checked the resistance of the heating element and it measures open circuit. I had the meter probes on the exposed ribbon tight against the edge of the glass. It appears that the heating element is blown. Short of connecting it to mains, I'm a bit baffled as to how anyone could blow the element as it shouldn't run particularly hot. I'm tempted to grind away some of the glass in case the ribbon has an invisible break just under the glass. But I'm uncertain as to how easy that would be and whether I might damage the whole screen.

I guess at this point I'm looking for some advice on what to do: try to repair or just treat it as a nice non-heated rear glass or any other ideas?

 

I have a heated rear screen in my S Type but unfortunately it does not work. When I rebuilt the car I checked the screen was working and found like you it was not so investigated. I found the wire taking power to the screen where it enters the screen had been broken off by the Jaguar specialist who had stripped the car down for the previous owners restoration. I tried in vane to re solder the external electrical wire to the internal filament wire but with no success so until I or the next owner wishes to replace the rear screen with a working one I get all fogged up in the winter.
Sad story is that I had two rear screens both heated and the first one worked fine until I tried to fit it. I had bought all new screen rubbers and fitted the front screen easily. When trying to fit the rear screen the damned thing would not sit properly in the rubber seal in one corner and whilst trying to hit the screen with the palm of my hand to get it in to the rubber seal I smashed the glass. I realised things were not right and a further investigation showed that the supplier I had bought the screen rubbers from had despite my explicit order of a rubber for a heated screen had sent me a non heated screen rubber. As you have stated above the rear heated screen is two layers of glass and is slightly thicker than a non heated screen so the non heated screen rubber is narrower. My attempts to force the thicker heated screen into the thinner rubber and then into the aperture were too much for the glass. So warning if you are changing from a non heated screen to a heated screen make sure you get the right sized rubber seal.

 

peter,
i think you answered your own question>> I've never had great use from heated windows as I keep my cars garaged;.......just because it's there doesn't always mean it's useful, 1st thing i do in an old car i own is disconnect the heated window, you can bet if you start messin" with the glass it will shatter on you

 

Originally the rear heated screen was permanently on from when the ignition was switched on. This caused a lot of flat batteries. I am not sure of the date but later cars were fitted with the rear screen pull on, push off switch. I used a spare rear screen switch to set up my choke on off switch. I know of a lot of early cars that have adopted an on off switch in different forms.

 

Rob, Tom, Thank you for your thoughts and good advice.

My HRW is still a nice screen in better condition than the one in the car so my plan is to use it even though it doesn't heat. I'll not risk destroying it in attempting a repair. From Rob's photo, it looks like an advantage of the HRW is that it doesn't produce a mass of small pieces of glass if it breaks. Since they aren't easy to install, that's significant. The suppliers don't seem to mention or list different rubber seals for the different thickness of glass so that's useful to know. If mine broke during installation, I'd go for a polycarbonate replacement. The usual sources have HRWs at prices that are rather high (for me), a hundred times my secondhand one and more than I've paid for cars in the past!