Narrative:

I met aircraft X at the gate. Aircraft has 1300 hours at ZZZ1. Crew left flight discrepancy on log page. 'At cruise; a system electric low pressure light illuminated pressure and quantity normal.' troubleshot 'a' electric hydraulic system in cockpit. All circuit breakers checked good. Cleared ground with fellow mechanic and placed 'a' electric hydraulic pump switch to 'on'-- no amp draw; no pressure indication; low pressure light on. Ground mechanic confirmed 'a' electric hydraulic pump not running. Consensus agreement amongst mechanics to reset 'a' electric hydraulic pump ground fault detector. Accessed ground fault detector reset switch behind circuit breaker panel and reset 'a' electric hydraulic pump ground fault detector per past maintenance practice. Cycled 'a' electric hydraulic pump switch to on and observed normal amp draw -- no excessive surge or spike. 'A' hydraulic system pressure at 3000 psi; low pressure and overheat lights not illuminated. Cycled system several times and all parameters normal. I observed system indications while fellow mechanic checked 'a' electric hydraulic system 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 mechanic continued to monitor 'a' electric hydraulic pump in wheel well for normal operation and temperature. After approximately 10 min operation without incident; I signed off discrepancy as 'reset ground fault detector; 'a' electric hydraulic system; checked good.' fellow mechanic checked 'a' electric hydraulic pump one final time for normal operation; overheat condition and cannon plug security -- all checked good. Aircraft X departed ZZZ1 en route ZZZ2. During climb out 'a' electric hydraulic system overheat light illuminated; followed by low pressure light. Performed QRH and turned off pump switch. During this time; speed trim; mach trim and automatic-slat fail lights illuminated. Discovered 'dim and test' circuit breaker P6-3 popped along with loss of most master caution system annunciators. Aircraft X declared an emergency and diverted to ZZZ3 without further incident. Mechanics sent from ZZZ1 to ZZZ3 to repair aircraft. Troubleshot and found cannon plug on 'a' electric hydraulic pump shorting out. Mechanics removed and replaced 'a' electric hydraulic pump and cannon plug. Mechanics removed and replaced overhead hydraulic control 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 hydraulic pump prior to resetting the ground fault detector per the fault isolation procedure boeing maintenance manual. Contributing human factor was my complacency; due to numerous past identical practices of resetting the ground fault detector; without disconnecting cannon plug per the maintenance manual without incident or repeat discrepancy. My complacency was the result of my lack of knowledge of the maintenance manual requirement; due to an accepted practice of resetting ground fault detector as a standard procedure. I acquired/learned of this procedure 20+ yrs ago; and did not reference the maintenance manual to verify the correct maintenance action.

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Original NASA ASRS Text

Title: 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.

Narrative: 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.

Data retrieved from NASA's ASRS site as of January 2009 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.