I installed my second Nest thermostat recently, this one was a little more involved because it was for a 7 wire heat pump.
The original wiring looked like this.
The Nest web site recommended this wiring. The only issue is that the Nest does not support a manual emergency heat wire so I had to leave that off. The Nest will still use emergency heat when necessary so I was not concerned about it.
My first attempt did not get all the wires in correctly.
After my first fix it still indicated an error.
After the fix the app showed it working.
Having 2 Nests make it possible to track usage throughout the house which was my goal.