A CHALLENGER 601 IN CRUSE AT FL400 DIVERTED AND SHUTDOWN #2 ENG DUE TO THE FUEL LOW PRESSURE WARNING LIGHT ILLUMINATED CAUSED BY A DISCONNECTED AND PLUGGED FUEL LINE.

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PERFORMING AN INTERNAL LEAK CHK ON R-HAND FIREWALL FUEL SHUTOFF VALVE REQUIRED DURING A SCHEDULED 4800 HR INSPECTION. I WAS INSTRUCTED PER MAINT MANUAL TO DISCONNECT FUEL TUBE FROM THE FUEL LOW PRESSURE WARNING SWITCH ON THE R-HAND ENG AND INSTALL PROTECTIVE COVERS; AS ONE OF THE MANY PROCS WHEN PERFORMING THIS TEST. I FAILED TO TAG THE LINE I HAD DISCONNECTED FROM THE FUEL LOW PRESSURE WARNING SWITCH; WHICH I USUALLY MAKE A COMMON PRACTICE TO DO. I FOUND WHEN PERFORMING THE LEAK TEST THAT THE R-HAND FIREWALL FUEL SHUTOFF VALVE WAS LEAKING BY. I SQUAWKED IT AND ORDERED A VALVE. THE VALVE WAS INSTALLED A COUPLE OF DAYS LATER BY ANOTHER MECH; AND I PERFORMED THE FUNCTIONAL TEST; LEAK TEST; AND CARRIED OUT THE ENG FUEL FEED LINE SHROUD PRESSURE TEST PER MAINT MANUAL -- FORGETTING ABOUT THE FUEL TUBE I HAD DISCONNECTED FROM THE FUEL LOW PRESSURE WARNING SWITCH. ANOTHER MECH (A QUALIFIED INSPECTOR) INSPECTED MY WORK BUT MISSED THE FUEL TUBE TO THE FUEL LOW PRESSURE WARNING SWITCH BEING DISCONNECTED. FURTHERMORE; 2 OTHER QUALIFIED INSPECTORS MISSED SEEING THE FUEL TUBE BEING DISCONNECTED -- 1 PERFORMING REQUIRED 4800 HR INSPECTION ITEMS ON R-HAND ENG AND 1 INSTALLING THE COWLINGS TO THE ENG; WHICH ALL COULD HAVE BEEN AVOIDED BY A SIMPLE RED TAG. ON JUN/XA/99; WE RAN THE ENGS AND LEAK CHKED AND OPS CHKED ALL SYS. THEN THAT EARLY EVENING WE HAD TO PERFORM A TEST FLT FOR 1 HR AND CLBED TO 16000 FT FOR A PRESSURIZATION TEST REQUIRED ON THE 4800 HR SCHEDULED INSPECTION. WE RECEIVED 'NO' LOW FUEL PRESSURE LIGHT DURING THIS TIME. WE LANDED AND DELIVERED THE ACFT THE NEXT MORNING (JUN/XC/99). THE CUSTOMER'S PLT TOOK THE PLANE AND PROCEEDED. ON THE WAY TO REACHING AN ALT OF APPROX FL400; THE PLT ENCOUNTERED A R ENG LOW FUEL PRESSURE LIGHT; WHICH REQUIRES THE PLT TO SHUT DOWN THE R ENG AND LAND ASAP; WHICH WAS IN ABC; US. UPON LNDG; THE PLT CALLED FBO AND TALKED TO A MECH THAT WAS INVOLVED WITH THE 4800 HR INSPECTION. UPON HEARING THE SQUAWK; OUR MECH DIRECTED THE PLT ON SOME POSSIBILITIES; WHERE IN TURN; THE MECHS AT ABC FBO FOUND THE CAPPED FUEL TUBE LINE TO THE R-HAND FUEL LOW PRESSURE WARNING SWITCH AND RECONNECTED -- RETURNING THE ACFT TO SVC.