A B727-200 WAS DISPATCHED IN NON COMPLIANCE WITH FUEL QUANTITY INDICATORS FOR TANKS #2 AND #3 SWAPPED DURING MAINT.

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MAINT HAD REMOVED THE FE'S DIGITAL GAUGE EQUIPPED FUEL PANEL TO FIX A PREVIOUS PROB. AFTER REINSTALLATION; THE FE RAN A FULL; FIRST FLT OF THE DAY TEST ON THE PANEL; AND RPTED EVERYTHING APPEARED NORMAL. FUEL LOADS IN ALL TANKS WERE EQUAL ON OUR FIRST LEG; SO THE ACFT APPEARED NORMAL INFLT; TOO. THE SECOND FLT THE NEXT MORNING ALSO STARTED NORMALLY; INCLUDING A NORMAL FIRST FLT OF THE DAY FUEL PANEL CHK. DURING CLBOUT; THE FE ENCOUNTERED UNUSUAL DIGITAL FUEL READOUTS WHILE ATTEMPTING TO CORRECT A MINOR IMBAL BTWN #1 AND #3 TANKS. HE ALSO RPTED THAT THE ANALOG BAR GRAPH READOUT FOR THE #3 TANK WAS WAY OUT OF LINE WITH THE READINGS IN THE #1 TANK. AS A RESULT; WE SUSPECTED CONNECTIONS MIGHT HAVE BEEN SWITCHED BTWN THE #2 AND #3 TANK GAUGES. WE MADE A QUICK CHK BY OPENING ALL THE XFEED MANIFOLD VALVES TO SEE WHICH GAUGE CONTINUED TO DROP. IN THIS CONFIGN; WITH ALL PUMPS ON; ONLY THE #2 TANK WOULD SHOW A FUEL BURN. HOWEVER; ONLY THE #3 TANK INDICATED FUEL WAS BEING BURNED. THE CAPT THEN CONTACTED COMPANY MECHS BY RADIO AND CONFIRMED THAT IT WAS POSSIBLE TO CROSS-CONNECT THE CANNON PLUGS FOR THE GAUGES AND THEN GET READINGS SUCH AS WE WERE EXPERIENCING. BECAUSE THE GAUGES APPEARED TO BE READING NORMALLY; BUT SIMPLY IN REVERSE POS; AND BECAUSE A PREFLT FUELING SAFETY CHK DONE BY THE FUELER ALSO INDICATED THE GAUGES WERE READING RELIABLY SO THAT WE HAD NOT BEEN INCORRECTLY FUELED (DUE TO AN INITIALLY EQUAL LOAD IN ALL TANKS); THE CAPT ELECTED TO CONTINUE TO PLANNED DEST ASSUMING THE GAUGES WERE SWITCHED. WE LANDED WITHOUT FURTHER INCIDENT. AFTER LNDG; MAINT PERSONNEL CONFIRMED THAT THE GAUGES HAD INDEED BEEN CROSS-CONNECTED. THEY ALSO INDICATED TO THE CAPT THAT IT WOULD HAVE BEEN VIRTUALLY IMPOSSIBLE FOR THE ENGINEER TO SPOT THIS PROB SO LONG S EQUAL FUEL LOADS WERE BOARDED. ACTUALLY; THE FE'S QUICK INFLT INITIAL ANALYSIS PROBABLY PREVENTED A FUEL OUT OF BAL CONDITION ON OUR FLT AND ALSO PREVENTED US FROM UNKNOWINGLY PASSING THIS ACFT ON TO ANOTHER UNSUSPECTING CREW.