Perhaps this will help. This is the 911 Workshop
Manual Supplement XXXIX, 1981, page 0.1-3/85.
This basically extends the ’78 main diagram. The
prior diagrams only show the single stage rear
window heater. I think this is pretty accurate all
the way back to ’70 model. If you need, I can
post the connector locations.
“
"
© Dr. Ing. h.c. F. Porsche A.G.
If you need, I can e-mail you this at 9.2M resolution.
Do you need the wire colors made clearer?
Remember to note the error that Warren found
in the Rear Window Defogger Relay. This diagram
has the error.
I reverse engineered the relay. I confirm Warren’s
correction. I need to clean up the circuit diagram
and will post it here.
It will be helpful if you can photo-document the
wiring from your 911. This is an area that Porsche
was slightly shy on documentation. Images at the
switch and the connections to the window will help.
Best,
Grady
gradyclay@hotmail.com