As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AT POWER UP BEFORE TAKEOFF IN KEF, TAKEOFF WARN HORN CAME ON. AIRCRAFT WAS PROPERLY CONFIGURED. EXITED RUNWAY, CYCLED CONTROLS AND RUNUP, NO HELP. RETURN TO GATE. REMOVED CONNECTOR PLUG D4168P FOUND DIRTY. CLEANED CONNECTOR PLUG AND REINSTALLED. OPS CHECKED SYSTEM IAW MM 31-26-0. (M)