A B737-500 ACFT WAS DISPATCHED WITH IMPROPER MEL REFERENCE FOR A 'LEFT WING BODY OVERHEAT' LIGHT DURING 'AFTER ENGINE START FLOW' SEQUENCE.

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I WAS ASSIGNED THE EVENING SHIFT ON THE B-200/B-500 MAINT CTL DESK. I RECEIVED A CALL FROM A LINE MECH REQUESTING MEL XX (APU INOP). FURTHER DISCUSSION REVEALED THAT WHENEVER THE APU WAS OPERATING (BLEED ON OR BLEED OFF); THAT THE L WING BODY OVERHEAT LIGHT ILLUMINATED. HE STATED THAT THERE WERE NO LEAKS IN THE SYS. SINCE IT ONLY HAPPENED WHEN THE APU WAS RUNNING WE APPLIED MEL XX; AND ACFT DEPARTED ON FLT. THE TEAM LEAD (AUDITING THE MEL RUN) AND ANOTHER CTLR QUESTIONED ME ABOUT THE MEL. I HAD APPLIED THE WRONG MEL. AT THIS TIME I CONTACTED MAINT TO RECLASSIFY THE MEL TO YY (WING BODY OVERHEAT SYS-L). THIS WAS ACCOMPLISHED IN THE LOGBOOK ONCE THE ACFT ARRIVED. THE ACFT HAD FLOWN 2 FLT LEGS WITH THE WRONG MEL APPLIED. ACFT WAS REPAIRED THAT NIGHT; FOUND LOOSE CONNECTOR D1390 AND SECURED. THIS EVENT WAS AN ERROR ON MY PART. THINKING BACK I SHOULD HAVE SLOWED DOWN; CAREFULLY REVIEWED ALL APPLICABLE MEL'S; AND ASKED FOR ASSISTANCE FROM THE OTHER CTLRS. SUPPLEMENTAL INFO FROM ACN 744674: WE TOOK THE AIRPLANE FROM THE PREVIOUS CREW AND EVERYTHING WAS NORMAL UNTIL THE AFTER ENG START FLOW. DURING THE AFTER START FLOW; WE NOTICED THE L WING-BODY OVERHEAT LIGHT WAS ILLUMINATED. WE RAN THE L WING-BODY OVERHEAT CHKLIST THROUGH TURNING THE APU SWITCH OFF. AFTER A FEW SECONDS; THE LIGHT REMAINED ILLUMINATED; SO WE INFORMED MAINT AND RETURNED TO THE GATE. I DID NOT NOTICE WHEN THE LIGHT WENT OUT. HOWEVER; THE MECH ENTERED THE COCKPIT RIGHT AFTER ENG SHUTDOWN AND NOTED THE LIGHT WAS EXTINGUISHED AT THAT TIME. THE MECH TOLD US HE KNEW EXACTLY WHAT THE PROB WAS. NEXT; THE CAPT CONTACTED MAINT CTL AND DISPATCH WITH THE MECH; AND AN MEL WAS ISSUED FOR THE APU. IT SEEMED THAT ALL THE PROPER PEOPLE WERE IN THE LOOP AND THE MEL APPEARED ROUTINE TO ME. WE FLEW THE NEXT 2 LEGS WITHOUT USING THE APU; AND ALL OTHER OPS WERE NORMAL. THE NEXT DAY; THE OPS COORDINATOR CALLED THE CAPT TO INFORM HIM THAT THERE WAS A PROB WITH THE MEL AND ASSOCIATED WRITE-UP. A SECOND CALL TO THE OPS COORDINATOR CONFIRMED THAT THE MEL SHOULD HAVE BEEN ISSUED FOR A WING-BODY OVERHEAT AND NOT THE APU. THIS WAS A LEARNING EXPERIENCE FOR ME. BESIDES LEARNING WHICH MEL SHOULD HAVE APPLIED IN THIS PARTICULAR CASE; I WILL DOUBLE MY EFFORTS IN THE FUTURE TO ENSURE AN MEL PROPERLY MATCHES THE PROB AND CAUTION LIGHTS IN THE COCKPIT. I WILL BE ESPECIALLY VIGILANT TO ENSURE AN MEL CLOSELY MATCHES THE COCKPIT PROB AND INDICATIONS. ADDITIONALLY; I WILL CONTINUE TO APPLY A HEALTHY DOSE OF SKEPTICISM TO THE WRITE-UPS IN ORDER TO CATCH ERRORS AND OMISSIONS.