What was found
ON TAXIING, AFTER ENGINE START, FLIGHT CREW NOTED NR 1 AND NR 2 ISOLATION VALVES, PN DC26F14155, WOULD NOT CLOSE. FLIGHT CREW ELECTED TO RETURN TO GATE FOR CORRECTIVE ACTION. AIRCRAFT RETURNED TO GATE WITHOUT INCIDENT. DURING TROUBLESHOOTING, MAINTENANCE CREW IDENTIFIED INTERMITTENT CONTACT BETWEEN WIRING HARNESSES AND ISOLATION VALVES. CLEANED CANNON PLUG NR 1 AND NR 2 ISOLATION VALVES. OPS CHECKED BOTH ISOLATION VALVES. AIRCRAFT RETURNED TO SERVICE. (X)