1976 911 rear window

[76allseason]

While driving my 911 on these humid Summer evenings, I notice my rear window fogs up continuously. The car is bone dry inside and no other windows fog up. When I pull out the rear window defogger two clicks, the window does not de-mist. The heated drivers side mirror gets warm. The green switch light does go on. My questions are:

Any idea why the rear window (inside) is getting foggy? Heat from the engine in the back?

Since the drivers side mirror is getting warm, does that confirm that the electric window defogger is working too, but that the wires are 32 years old and are just not working properly anymore?

Solutions?

[ossiblue]

I think you answered your first question about why the window gets fogged. Why the defogger doesn't work is another matter. Several possibilities:
1. The rear seal has been replaced and the leads to the defogger were not routed through the seal and connected to the window because it is a royal PITA. (most likely case)
2. You have a bad relay. I believe it is located in the engine compartment fuse panel.
I'm sure there are other possibilities, but these two came to mind first.

[76allseason]

Thanks. I will check on things this evening.

[4sd911]

The defroster element in the window may be bad. The sun will at some point decay the "lines" across the window and it will no longer work.