As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
RETURN TO GATE DUE TO ELECTRICAL FUMES IN CABIN.APU AND LEFT ENGINE RUNNING. MOMENTARY LOSS OF ELECTRICAL POWER WITH EMERGENCY POWER COMING ON. EMERGENCY POWER IN USE LIGHT CAME ON WITH SWITCH IN ARM POSITION. APU HARNESS/STARTER AND R2-63 RELAY REPLACEMENT IN PROGRESS. REPLACED R2-63 RELAY P/MM AS SUGGESTED. OP CK/TEST NML. CLEANED AREA PER PROCESS STD 900-1-2-1 NR 4, NO OTHER DAMAGE NOTED.