The brand new C-141 was experiencing several maintenance difficulties. The right extended range tank fuel gauge was erratic, and the AC ‘power on’ light was inoperative. A maintenance crew was sent to rectify both problems. A team began to work in the flight deck to check the power on light. Other technicians began to work on the fuel gauge. However, the fuel tank was not yet fully defueled. One of the electrical technicians connected the tester to the fuel tank, but failed to ground the test equipment. Another technician plugged an extension cord into the external 115V AC receptacle of the APU. A short in the shielding of the cables connected to the fuel tank caused a spark within the nearly empty tank. The right wing exploded. Two technicians were killed almost immediately. One of the technicians in the cockpit was fatally burned while exiting the right troop door into a burning pool of JP-4 fuel.