What was found
BTB PROBE HEAT EICAS MSG AND L AUX, FO PITOT, TAT ON OVERHEAD LT PANEL AFTER ENG START WITH APU SHUT DOWN (TAT ON EICAS TEMP INDICATION FLUCTUATING TO +100 C). PERFORMED FIM 30-31-0 SWAPPED RELAYS K522 AND 515, K514 AND K517, H646 AND K644, NO HELP. ON GROUND DISCREET LIGHTS "CAPT PITOT", RT AUX PITOT, L AOA, AND TAT DO NOT ILLUMINATE. AFTER ENG START, F/O PITOT, LT AUX PITOT DO NOT EXTINGUISH. SUSPECT PSEU. TAT BREAKER PULLED BECAUSE RAT HEATS WITH ENG OFF. TROUBLESHOT SYSTEM IAW WDM 32-09-12,32-09-13, AND 30-31-11. FOUND SWITCH S10598 TO BE BAD. PULLED CIRCUIT BREAKER L-PITOT HEATER INDICATION ON PH-1. RESET L-PITOT HEATER INDICATION C/B ON P11-1. REINSTALLED ALL RELAYS REMOVED FOR T/S AND REINSTALLED WIRING GOING TO D1 OF K552 AND TB188 XC-7 AS PER WDM 32-09-13 AND SWPM 20-50-01. REMOVED AND REPLACED S10598 AND PERFORMED GOOD, OPS CHECK OF S10598 PER MM 32-09-07. PERFORMED ENG RUN PER 71-00-00 TO VERIFY NORMAL INDICATION. NO EICAS MESSAGES.