As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
SET PARKING BRAKE AFTER PUSH BACK BUT NO PARK BRAKE LT ILLUMINATED AND NO PARK BRAKE ON EICAS APPEARED. AIRCRAFT BACK TO BLOCK AND GROUNDED BY MAINTENANCE. MAINTENANCE CLEANED CANNON PLUG OPERATED BRAKES SEVERAL TIMES OPS CK NORMAL IAW 32-44-00. AIRCRAFT RETURNED TO SERVICE.