A B737 ON TKOF ROLL REJECTED THE TKOF AT 55 KTS DUE TO TKOF WARNING HORN SOUNDING CAUSED BY MALFUNCTIONING LEADING EDGE SLAT POS INDICATIONS.

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THROTTLES ADVANCED FOR TKOF TO TKOF WARNING HORN SETTING JUST PRIOR TO ENGAGING TOGA BUTTON. TKOF WARNING HORN SOUNDED. REDUCED PWR JUST BELOW HORN LEVEL AND HIT SPD BRAKE HANDLE TO INSURE FULL RETRACTION. ADVANCED THROTTLES AND HORN RESOUNDED. TKOF REJECTED. EXITED RWY AT HIGHSPD. ACFT PARKED AND REJECTED TKOF CHKLIST COMPLETED. ANALYSIS OF PROB RESULTED IN NOTICE THAT GREEN LEADING EDGE DEVICE EXTENDED LIGHT EXTINGUISHED. NO LIGHTS ON OVERHEAD. TEST OF LIGHTS INDICATED LEADING EDGE DEVICES RETRACTED. SAME WERE VISUALLY EXTENDED AT FLAPS 5 DEG POS. RETRACTED FLAPS TO ZERO. NO AMBER IN-TRANSIT LIGHT OR OVERHEAD INDICATIONS OF TRANSIT. RE-EXTENDED FLAPS TO 5 DEGS WITH NO LEADING EDGE DEVICE INDICATIONS. TESTED ALL LAMPS OK; CHKED CIRCUIT BREAKER PANEL AND FOUND NO BREAKERS POPPED. FLAP POS AND GREEN LEADING EDGE DEVICE EXTENDED LIGHT HAD BEEN VERIFIED BY BOTH PLTS ON TAXI OUT AS PART OF TAXI CHKLIST. CONTACTED STATION AND MAINT AND RETURNED TO GATE. AFTER RETURN TO THE GATE; MAINT TRIED TWICE WITH SAME RESULT BOTH BEFORE AND AFTER PUSHING ON ALL ROWS OF CIRCUIT BREAKERS. SUDDENLY; THE FLAP POS INDICATORS CYCLED TOWARD ZERO AND BACK TO 5 DEGS WITH NO HANDLE MOVEMENT. IMMEDIATELY; PROPER LEADING EDGE DEVICE INDICATIONS APPEARED. TEST OF TKOF WARNING SYS WAS NORMAL FOR CONFIGN - FLAPS 5 DEGS (NO HORN). FLAPS WERE CYCLED AND TKOF WARNING SYS TESTED SEVERAL TIMES WITH NORMAL OPERATING RESULTS. MAINT CLRED LOGBOOK AND FLT CONTINUED WITHOUT INCIDENT.