What was found
APU FAULT LIGHT ON START. FOLLOWED QRH PROCEDURES. STILL HAD FAULT LIGHT. ACFT GROUNDED. ON APU START UP, FOUND FAULT 49-41180, IGNITION UNIT CIRCUIT SHOWS HIGH CURRENT. IAW FIM 49-40 TASK 804, REPLACED EXCITER UNIT IAW AMM 49-41-31. TO ADDRESS PREVIOUS FAULT 49-41011, NO FLAME SHUTDOWN, ALSO REPLACED APU IGNITER PLUG IAW AMM 49-41-51, AND IGNITER PLUG LEAD IAW AMM 49-41-52. ALL FAULTS CLEARED. APU OPERATES NORMAL IAW AMM 49-11-00.