What was found
IMMEDIATELY AFTER SETTING TAKEOFF POWER ON RUNWAY "PARKING BRAKE" CAUTION LIGHT ILLUMINATED AND T/O WARNING HORN SOUNDED. LIGHT AND HORN EXTINGUISHED AS SOON AS POWER WAS REDUCED FOR T/O ABORT. ABORTED TAKE OFF. REMOVED FROM SERVICE. REMOVED CENTER CONSOLE ACCESS PANEL ON L/H SIDE TO PERFORM GVI OF PARK BRAKE QUADRANT. FOUND DEBRIS AND DUST ON MICROSWITCHES. REMOVED DEBRIS AND CLEANED MICROSWITCHES AND QUADRANT. REINSTALLED CENTER CONSOLE L/H SIDE ACCESS PANEL. PERFORMED FUNCTIONAL TEST OF TAKE-OFF WARNING SYSTEM MULTIPLE TIMES. REF: Q400 AMM TASK 31-52-00-720-801. FUNCTIONAL TEST CHECKED GOOD, MULTIPLE TIMES. NO PARTS REPLACED. AIRCRAFT RETURNED TO SERVICE.