A B737-300 ACFT DECLARED AN EMERGENCY DURING CLIMBOUT WHEN 'A' SYSTEM 'ELECTRIC' PUMP OVERHEAT AND LOW PRESS LIGHT ILLUMINATED. LOST MOST OF MASTER CAUTION SYS ANNUNCIATORS.

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I MET ACFT X AT THE GATE. ACFT HAS 1300 HRS AT ZZZ1. CREW LEFT FLT DISCREPANCY ON LOG PAGE. 'AT CRUISE; A SYS ELECTRIC LOW PRESSURE LIGHT ILLUMINATED PRESSURE AND QUANTITY NORMAL.' TROUBLESHOT 'A' ELECTRIC HYD SYS IN COCKPIT. ALL CIRCUIT BREAKERS CHKED GOOD. CLRED GND WITH FELLOW MECH AND PLACED 'A' ELECTRIC HYD PUMP SWITCH TO 'ON'-- NO AMP DRAW; NO PRESSURE INDICATION; LOW PRESSURE LIGHT ON. GND MECH CONFIRMED 'A' ELECTRIC HYD PUMP NOT RUNNING. CONSENSUS AGREEMENT AMONGST MECHS TO RESET 'A' ELECTRIC HYD PUMP GND FAULT DETECTOR. ACCESSED GND FAULT DETECTOR RESET SWITCH BEHIND CIRCUIT BREAKER PANEL AND RESET 'A' ELECTRIC HYD PUMP GND FAULT DETECTOR PER PAST MAINT PRACTICE. CYCLED 'A' ELECTRIC HYD PUMP SWITCH TO ON AND OBSERVED NORMAL AMP DRAW -- NO EXCESSIVE SURGE OR SPIKE. 'A' HYD SYS PRESSURE AT 3000 PSI; LOW PRESSURE AND OVERHEAT LIGHTS NOT ILLUMINATED. CYCLED SYS SEVERAL TIMES AND ALL PARAMETERS NORMAL. I OBSERVED SYS INDICATIONS WHILE FELLOW MECH CHKED 'A' ELECTRIC HYD SYS PUMP CANNON PLUG FOR SECURITY (SHAKE TEST) AND EVIDENCE OF ARCING OR SHORTING ON CANNON PLUG WITH CANNON PLUG ON PUMP. ALL COCKPIT INDICATIONS NORMAL. FELLOW MECH CONTINUED TO MONITOR 'A' ELECTRIC HYD PUMP IN WHEEL WELL FOR NORMAL OP AND TEMP. AFTER APPROX 10 MIN OP WITHOUT INCIDENT; I SIGNED OFF DISCREPANCY AS 'RESET GND FAULT DETECTOR; 'A' ELECTRIC HYD SYS; CHKED GOOD.' FELLOW MECH CHKED 'A' ELECTRIC HYD PUMP ONE FINAL TIME FOR NORMAL OP; OVERHEAT CONDITION AND CANNON PLUG SECURITY -- ALL CHKED GOOD. ACFT X DEPARTED ZZZ1 ENRTE ZZZ2. DURING CLBOUT 'A' ELECTRIC HYD SYS OVERHEAT LIGHT ILLUMINATED; FOLLOWED BY LOW PRESSURE LIGHT. PERFORMED QRH AND TURNED OFF PUMP SWITCH. DURING THIS TIME; SPD TRIM; MACH TRIM AND AUTO-SLAT FAIL LIGHTS ILLUMINATED. DISCOVERED 'DIM AND TEST' CIRCUIT BREAKER P6-3 POPPED ALONG WITH LOSS OF MOST MASTER CAUTION SYS ANNUNCIATORS. ACFT X DECLARED AN EMER AND DIVERTED TO ZZZ3 WITHOUT FURTHER INCIDENT. MECHS SENT FROM ZZZ1 TO ZZZ3 TO REPAIR ACFT. TROUBLESHOT AND FOUND CANNON PLUG ON 'A' ELECTRIC HYD PUMP SHORTING OUT. MECHS REMOVED AND REPLACED 'A' ELECTRIC HYD PUMP AND CANNON PLUG. MECHS REMOVED AND REPLACED OVERHEAD HYD CTL MODULE AND CASE DRAIN FILTERS. DURING REVIEW OF EVENT ON JUL/XA/07; I DISCOVERED THAT I DID NOT DISCONNECT THE CANNON PLUG ON THE 'A' ELECTRIC HYD PUMP PRIOR TO RESETTING THE GND FAULT DETECTOR PER THE FAULT ISOLATION PROC BOEING MAINT MANUAL. CONTRIBUTING HUMAN FACTOR WAS MY COMPLACENCY; DUE TO NUMEROUS PAST IDENTICAL PRACTICES OF RESETTING THE GND FAULT DETECTOR; WITHOUT DISCONNECTING CANNON PLUG PER THE MAINT MANUAL WITHOUT INCIDENT OR REPEAT DISCREPANCY. MY COMPLACENCY WAS THE RESULT OF MY LACK OF KNOWLEDGE OF THE MAINT MANUAL REQUIREMENT; DUE TO AN ACCEPTED PRACTICE OF RESETTING GND FAULT DETECTOR AS A STANDARD PROC. I ACQUIRED/LEARNED OF THIS PROC 20+ YRS AGO; AND DID NOT REF THE MAINT MANUAL TO VERIFY THE CORRECT MAINT ACTION.