What was found
ON CLIMB THRU 26,000 THE MAIN CARGO DOOR SYSTEM "A" LIGHT ILLUM. THE SENSORS MUNE ON ACARS POPPED UP INDICATING MAIN CARGO DOOR OPEN. ABOU T 20 SECONDS LATER TWO BANGS WITH ACCOMPANING YAW. A/C PRESS STARTED T O CLIMB. SLOWED A/C AND STARTED DESCENT. ON FINAL APPROACH ALL THE IN DICATOR LIGHTS WENT OUT. REMOVED AND REPLACED 51-256 DOOR SWITCH IAW UPS DC8 M.M. 32-70-00. PRESSURIZED A/C UP TO 8.2 PSI IAW UPS DC8 M.M. 21-10-00. MCD "A" SYS LIGHT DID NOT ILLUMINATE AND OPS CHECKED GOOD IAW UPS DC8 M.M. 52-70-00. N/R 632638