AN MD80 WITH A FLT CREW RPT OF L MAIN GEAR RED LIGHT ILLUMINATED WITH THE GEAR HANDLE UP. TECHNICIAN MADE ALL CHKS REQUIRED PER MAINT MANUAL. DID NOT SIGN OFF RPT BECAUSE PREVIOUS ENGINEERING BULLETIN REQUIRES GEAR SWITCH IF NO POSITIVE FAULT FOUND. NOTIFIED BY ENGINEER BULLETIN NO LONGER IN EFFECT.

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ON MAR/THU/06; I WAS ASSIGNED TO ACFT INBOUND TRIP. THE CREW HAD SENT A MESSAGE INDICATING THE L MAIN LNDG GEAR INDICATED RED WITH THE HANDLE UP. UPON FLT CREW DEBRIEF FROM MYSELF; THE CREW TOLD ME THEY HAD A RED GEAR LIGHT ON RETRACTION AFTER TKOF AND IT STAYED ON UNTIL THE GEAR HANDLE WAS PLACED TO THE DOWN POS AND BACK TO THE UP POS. THEN THE LIGHT EXTINGUISHED; AND STAYED OUT THE REST OF THE FLT. AFTER I DEBRIEFED THE CREW; I INSPECTED THE L MAIN LNDG GEAR UPLOCK SENSOR AND UPLOCK MECHANISM AND ASSOCIATED WIRING AND FOUND NO NOTICEABLE DEFECTS. I THEN WENT TO THE 'PROX BOX' AND CHKED THE UPLOCK SENSOR AND IT INDICATED A 'PASS' AND A FAR INDICATION. THE PROX BOX WAS THEN REMOVED AND THE SENSOR AND ASSOCIATED WIRING WAS CHKED WITH AN INDUCTANCE METER AND THE SENSOR PASSED BOTH NEAR AND FAR INDUCTANCE TESTS ACCORDING TO BULLETIN. AFTER ALL THESE TESTS PASSED; I INDICATED TO SUPVR THAT THE ACFT REQUIRES A GEAR SWING FOR ME TO SIGN THE ITEM OFF. I WAS ASKED IF ALL OF THE TESTS PASSED AND I STATED THAT EVERYTHING TESTED GOOD; BUT STILL REFUSED TO SIGN THE ITEM OFF DUE TO A LETTER ISSUED IN 1990 (LETTER ENCLOSED) BULLETIN #X STATING THAT ALL LNDG GEAR INDICATION ITEMS REQUIRE A RETRACTION CHK IF NO POSITIVE FIX IS FOUND. THE ITEM WAS THEN SIGNED OFF BY SOMEONE ELSE. A FEW DAYS LATER; I WAS SHOWN AN E-MAIL FROM A LEAD ENGINEER ON MAR/MON/06; STATING THAT THE BULLETIN IS A DINOSAUR AND NO LONGER IS IN EFFECT AND HAS BEEN SUPERSEDED BY OTHER DOCUMENTATION THAT STATES NO RETRACTION TEST IS REQUIRED. (E-MAIL LETTER IS ENCLOSED). HOW IS A MECH SUPPOSED TO PROVE THAT A POSITIVE OPS CHK HAS BEEN ACCOMPLISHED WITHOUT SWINGING THE GEAR? SHOULDN'T THERE BE A REF STATING THE REQUIREMENTS WHEN A POSITIVE FIX IS NOT FOUND? I WOULD THINK ALL OF THIS WOULD AFFECT THE AIRWORTHINESS OF THE ACFT. THERE ARE CONFLICTING IDEAS BTWN PEOPLE ON WHETHER AN ACFT REQUIRES A RETRACTION CHK OR NOT WHEN AN INDICATION PROB CANNOT BE DUPLICATED. THERE IS NO MAINT MANUAL OR GPM REFS.