What was found
AFTER TAKE OFF THROUGH CLIMB AND CRUISE, LT - DUCT PRESSURE READ 6 PSI AND RT - DUCT PRESSURE WAS 45 PSI. 2.5 HOURS INTO FLT, LT - DUCT PRESSURE CAME UP TO READ EVEN WITH RT SIDE. AFTER 10 MINUTES PRESSURE SPLIT REOCCURED AT CRUISE 32,000 FT WITH LT -DUCT AT 22 AND RT AT 48 PSI. ACFT GROUNDED. PERFORMED FIM TASK 36-10 TASK 808 - PRESSURE INDICATIONS NORMAL. PERFORMED ASA TASK 36-00-00-860-807 - ALL CHECKED NORMAL. WHILE COMPLETING MAINTENANCE INSPECTIONS FOUND CONNECTOR PLUG DP 1102 DISCONNECTED FROM NR 1 ENG BLEED AIR REGULATOR. RECONNECTED CONNECTOR PLUG DP 1102 AND OPERATED ENGINE, BLEED AIR PRESSURE IN LIMITS AT IDLE SPEED.