there's a small orifice that bleeds off pressure (with the solenoid on) and lets the wastegate see less pressure than you're boosting which in turn opens the wastegate at a later time so that you can boost higher than the wastegate's rated setting. With the solenoid off the wastegate will open at it's rated setting because it will see all of the pressure you're boosting. I would guess that the wastegates on your turbos are rated to open at 10 psi and he set them up to see all of the charge pipe pressure so if you activate the boost control solenoid it would bleed off boost and trick your wastegates into opening at a higher boost. I would recommend you leave them disconnected until you've upgraded your injectors and learned enough about turbos.
"The dreaded 2nd windshiled wiper swipe when you turn it off its almost like tis showing you that it's boss, and it doesn't have to stop when you tell it to :("-College Boy
