You need
access to a wiring diagram?
I
found the boost signal is coming from the PCM (Powertrain control module/ engine control module)
C3 connector pin 10 is a tan wire that needs to go to your boost gauge.
GM calls the OBDII port the DLC (data link connector).
I
found it gets power from Lighter fuse on pin 16, a red/white wire.
That same diagram has pin 1 of the DLC as the green GM low speed LAN wire that goes to the BCM and IPC.