If you want to implement ECU-controlled boost control on your single-port wastegate then you will need one of these.  If you are using a dual-port solenoid and want to implement even finer-resolution boost control by controlling the dome pressure, then you will either need two of these or go with the Holley High-Flow Dual-Solenoid Boost Control Kit.

Holley has written a book on ECU control of boost--literally.  And we provide that below, along with a step-by-step example.  Don't miss this great resource available for free download.

 
User Manual
Implementing Boost Control with Holley ECU

 
Step-By-Step Example
Implementing Boost Control with Holley ECU