What was found
CAPTAIN'S NAV FLAGGED ON HSI AFTER TAKEOFF. THIS WAS FOLLOWED BY NUMEROUS CIRCUIT BREAKERS POPPING INCLUDING THE LEFT AC BUS C-PHASE. FLIGHT RETURNED TO DTW AND LANDED WITHOUT INCIDENT. MAINTENANCE REPLACED BOTH A AND C PHASE CIRCUIT BREAKERS FOR LEFT AC BUS. FOUND ALL PHASES OF CENTER FORWARD FUEL BOOST PUMP CIRCUIT BREAKERS POPPED. THIS IS THE SUSPECTED CAUSE FOR THE LEFT AC BUS CIRCUIT BREAKER POPPED. REPLACED CENTER FORWARD FUEL BOOST PUMP. LEAK AND OPERATIONAL CHECK NORMAL.