You'll be looking for a blue wire at the rear wiper motor connector, I believe. I ran mine from the front, a bit fiddly getting it through the flexible shroud at the top of the tailgate, but it can be done.
Unless it's changed in later models, the electric heater is best thought of as kettle elements heating water. That's why it takes a while to blow warm!
Tracing these circuits back, they're all fed from an 80 Amp fusible link, connected to the auxillary battery positive terminal. If everything else is working, it looks like a bad connection, or a bad ETACS unit.