What was found
DURING CLIMB PASSING 350, NOTICED LEFT EGT WAS LESS THAN 1/2 OF NORMAL. SEI SHOWED 40-46 REGARDLESS OF POWER SETTING.AIRCRAFT PROCEEDED WITH A AIR TURNBACK WITHOUT EVENT. AIRCRAFT WAS GROUNDED BY MAINTENANCE. MAINTENANCE FOUND THERMOCOUPLE HARNESS CONNECTOR BROKEN AT 11'OCLOCK POSITION. REMOVED AND REPLACED UPPER HARNESS IAW B767 77-21-03.CONDUCTED L ENGINE RUN FOR EGT INDICATION CHECK PER ABX ERU/TAXI CHECKLIST AND AMM 77-21-00. NO HELP. DISCONNECTED STANDBY ENGINE INDICATOR, EICAS EGT NORMAL. FOUND PUSHED PIN ON SEI L/H ENGINE CONNECTOR TO GROUND. RESEATED PIN, ALL EGT INDICATIONS NORMAL AND MATCHING. REF WDM 77-21-11 AND AMM 77-41-01. SEI OPS CHECK OK. AIRCRAFT RETURNED TO SERVICE.