What was found
AFTER PERFORMING A NO BLEED TAKEOFF AND WHILE REESTABLISHING NORMAL CONFIGURATION, THE LEFT DUCT WAS PRESSURIZED REGARDLESS OF SWITCH POSITIONS, - ISOLATION VALVE CLOSED, APU AND #1 BLEED OFF, LEFT DUCT STILL PRESSURIZED. NEEDLE NOT STUCK. WE DID SEE SLIGHT MOVEMENT. GROUNDED - YES. FOUND #1 ENG BAR CANNON PLUG DISCONNECTED. RECONNECTED CANNON PLUG TO BLEED AIR REGULATOR REF B737-900 AMM 73-21-06-400-802-F00. GROUND VERIFICATIONS IDLE ENGINE RUN/ OPS CHECK GOOD AND ACCOMPLISHED.