have recently check code on ang cel on a legacy gtb. Where is this located ? what can be done to fixed this problem?

code 66 - air assist solenoid valve low input??? what does this look like?: hope you guys could help me out on this problems

Forgot to mention this car was convert to single turbo using wrx exhaust manifold n turbo.
So i have no idea how the vaccum goes. It is running a manual boost controller so it should be a problem with the wasteagte