Here is a file showing the vacuum routing schematics for 1968 - 1972 Mustangs. These came from Mustang Barn, and offered for free download. I, with their permission, assembled all of their schematic files into a single PDF, grouped and sorted by year, and by engine size.
For 1973 Mustang/Cougar the Forel Shop Manuals have all the relevant emission control systems, and nearly all vacuum schematics, for 1973 in Volume 6 of said Shop Manual. Here is the link to their eBooks site for 1973:
There are two calibrations missing from their 1973 Shop Manual Volume 6 vacuum schematics. One is for the 351C 4v with manual transmission, the other is for the 351C 4v with automatic transmission. Both of those calibrations are attached in a single PDF to this post also.
I also attached another PDF with more info on these Thermal Vacuum Switches, and how they are used. That file references 1971 engines, but the info can be used across many years of similar equipment.