What was found
SEAT 33DEF TO 38DEF EMERGENCY LIGHTS DO NOT ILLUMINATE WHEN SET TO ON. WCU AT THE SEAT PAN 43D SWAPPED TO WCU AT SEAT PAN 39D, MAINT MSG:33-11726 WAS ERASED. NEW WCU REPLACED ON SEAT PAN 39D. ORIGINAL WCU ON SEAT PAN 43D RESTORED BACK. MAINT MSG:33-13126 TRIGGERED AFTER WELS SYS STABILIZED. WCU SOFTWARE LOADING CARRIED OUT IAW AMM B787-A-33-51-07-04A-750A-A INTO PRIMARY WCU AT DOOR 1L,2R,3L,4R. SOFTWARE CONFIGURATION CHECKED & MAINT MESS 33-13126 CLEARED. EMERGENCY LIGHTS OPS TESTED SATISFACTORY.