My car has an Auto Meter Nexus Series Vacuum/Boost gauge (electric). In this picture you can see where I taped into the Vacuum line on the driver's side, with a "T" tap and a vacuum line to the gauge sender that I mounted on the cowl.
Good luck with your install!
MOTM winner May 2015 "Best mods Mustang". Please View my Garage for complete details on modifications.