What was found
SHORTLY AFTER REACHING TOP OF CLIMB, FL360, MAIN CARGO DOOR EICAS MESSAGE ILLUMINATED ALONG WITH ASSOCIATED CARGO DOOR DISCRETE LIGHT. WE ACCOMPLISHED THE CHECKLIST AND DESCENDING THROUGH 15000FT THE LIGHTS WENT OUT. EMERGENCY DECLARED. COMPLETED SENSOR INSTALLTION OPS CHECK FROM 52-71-09-2 9.C.(4) TO END. OPS CHECKS/TESTED GOOD. ALSO COMPLETED THE BREAKOUT BOX TEST OF MAIN CARGO DOOR SENSOR REQUESTED. 31-70-05-5-99 AND 31-70-06-6-99 - TESTED/ PASSED. MAIN CARGO DOOR LATCHED AND LOCK INDICATION TEST GOOD/PASSED.