What was found
REJECTED TAKEOFF AT 73 KTS DUE TO DOOR AFT CARGO EICAS. OPTIONAL LARGE AFT CARGO DOOR INDICATION SYSTEM FAULT DETECTED. VERIFIED AFT CARGO WAS CLOSED, LATCHED & LOCKED CORRECTLY. FDE SHOWS FAULT 52-11960 ACTIVE. CYCLED AFT CARGO DOOR OPEN & INSPECTED CAMS, & ASSOC. PINS ALL CLEAR & OPS NORMALLY, ALL OK. CLOSED AFT CARGO DOOR & EICAS MSG CLEARED & DOOR INDICATION SHOWS AFT CARGO DOOR CLOSED. IAW AMM 52-34-00 & 52-37-00. PLACIED ON MEL AS A PRECAUTION. AFT CARGO DOOR INDICATION INOP IAW MEL 5271C. MAINT. PROCEDURE PARA. A (1-9) AND PARA. B. R & R AFT CARGO DOOR RIBBON HARNESS IAW AMM 52-37-23-900-801. OP CHECK AFT CARGO DOOR OPEN & CLOSE GOOD. NO FAULT INDICATED.