What was found
LOWER AFT BODY OVERHEAT LIGHT ILLUMINATED 5 MINUTES AFTER SWITCHING LEFT AIR CONDITIONING PACK FROM NR 1 TO NR 2 ENGINE. CHECKLIST COMPLIED WITH LIGHT WENT OUT AFTER CLOSING NR 1 START LEVER. RAN ALL 3 ENGINES WITH ALL BLEEDS OPEN AND BOTH PACKS ON COULD NOT DUPLICATE. ENGS WERE AT 65 PERCENT N2. FOUND NO LEAKS IN AFT AIRSTAIR OR NR 1 PACK AREA. DETECTOR LOOPS OK, FOUND 1819 BULB IN LIGHT ON S/O PANEL. REPLACED WITH 1864, RAN ENGINES TO TAKEOFF POWER WITH BLEEDS OPEN AND PACKS ON, OPERATION OK.