I realize this is an older thread but wanted to share my findings. I had the same issue and went through all the troubleshooting procedures described in the turbo regal repair manual. This includes checking the pin switches and door lock switches. Ended up being the ignition warning buzzer...
Purchased some vac brake conversion parts this past week and could not be happier about the transaction. Parts were just as described, shipped quickly with good communication. Would be happy to do business with again. Thanks!
Message sent regarding these two items
-Autometer Boost gauge with A pillar single pod $25
-Vac brake set up $100+shipping(master cylinder, power brake booster, and correct pedal)