For Anyone who may need this info for a 71 firebird formula with A/C. Port 1 White, Port 2 Brown, Port 3 Black(Engine Vacuum), port 4 is Blue, Port 5 is Gray which goes to port 2 of 3 port switch, Gray continues from Port 1 of 3 port switch to heater control Valve as long as you don't have a red hose, 6 is open, port 7 is yellow, port 8 open, port 9 open.
I have a 72 Formula 350 w/AC and have been scouring the internet for a 72 vacuum diagram. Have been using a 78 (5-port switch).
Yesterday I found another (yellow?) vacuum line and don't know where it goes. I have the white, brown, black, blue, gray and now 2
yellow. Sheesh. Will try your hookup and see how that works. Will also determine if my 72 has the secondary vacuum switch for the
heater valve. Of that I don't know. FYI: the port assignements on the 78 diagram are: port 1 open, port 2brown (kick panel), port 3 (black vac source),
port 4 blue defrost, port 5 yellow diverter door, port 6 white AC diverter door. ports 7,8,9, open. My port six goes to the door on the upper cowl
which you can see with the hood up. Ordered an assembly manual, and a electrical/vacuum diagram manual specifically for the 72 model year.
Be interesting to see what that holds. I'm using a "reconditioned" vacuum switch which I'm not sure is totally reconditioned but that jury is still
out. Thanks much for the input. Much appreciated.
Tonino