As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
#1 TRANSFER BUS OFF LIGHT ILLUMINATED WHEN POWER WAS TRANSFERRED FROM ENG DRIVEN GENERATOR TO APU GEN WHEN TAXING IN POST FLIGHT SAME ISSUE APPEARED WHEN GRD POWER WAS APPLIED TO THE JET. GROUNDED - YES. PERFORMED B737-900 FIM TASK 24-21 TASK 822 FOUND BUS TIE BREAKER STUCK. RESET THE BUS TIE BREAKER FOR THE NUMBER ONE SIDE TRANSFER BUS OFF LIGHT REMAINS EXTINGUISHED OPS CK NORMAL.