The manual boost controller is installed like this:
The original solenoid stays plugged in electrically, and its lower vacuum hoses stays plugged in as well.
Then you "tune" with the MBC, cranking it up slowly and seeing how much boost you can achieve before it hits fuel cut. Might be 15psi, might be less. Either way you'll get a couple PSI in there, and a quicker turbo spool to boot.