What was found
NR 2 ENGINE OVERHEAT ILLUMINATED ON GROUND. ASSOCIATED CONDITIONS WHEN OVHT DET SWITCH PLACED TO A LIGHT EXTINGUISHED AND FAULT ILLUMINATED. WHEN OVHT DET SWITCH PLACED TO B ENG 2 OVERHEAT REMAINS ILLUMINATED. WHILE ON DEFERRAL, ON THE FOLLOWING FLIGHT SITTING AT THE END OF THE RUNWAY AWAITING FOR DEPT. (WITH ENG. OVHT SYS A ON MEL) NR 2 ENG WITH OVHT SWITCH IN SYS B POSITION ENGINE OVHT LIGHT ILLUMINATED. ACFT GROUNDED. OVHT LT ON AT GATE, FIRE CONT MODULE FAULT LTS FLICKER BETWEEN UPPER LWR FAN ELEMENT IN LOOP A POSITION, AND DOES NOT TEST IN LOOP B POSITION - SHOWING LOW RESISTANCE. GVI, FOUND / CLEANED AND RESECURED NR 2 ENG. UPPER FAN FIRE DETECTOR, AFT HOUSING NUT FOR DETECTOR 2, UPPER LH WIRE HARNESS. FAULT LIGHTS EXTINGUISHED ON ENGINE/APU FIRE DETECTION CONTROL MODULE AND BITE TEST NORMAL, NO FAULTS. REF AMM 26-10 TASK 801. ENG & APU FIRE DETECTION OPS TEST NORMAL, REF AMM TASK 26-11-00-710-801 AND TASK 26-15-00-710-801.