What was found
SCC-1430L AVIONICS COOLING FAN INOP. (FIRE/SMOKE INFLIGHT AIR TURNBACK). AVIONICS COOLING FAN DEFERRED AND THEN REPLACED WHEN AIRCRAFT RETURNED TO BASE. UPON FURTHER INVESTIGATION FOUND NR 2 ENGINE AUTO IGNITION SYSTEM INOP. REPAIRED WIRE 20004A20 IN 2 PLACES, ONE AT 2' BEHIND NR 2 NH INDICATOR. ANOTHER AT CLOSET CEILING UNDER PA AMP WERE IT RUBBED THROUGH. TEST GOOD MM# 74-00-00. AUTO IGNITION WIRES ARE BELIEVED TO BE THE ORIGINAL CAUSE OF THE SMOKE IN CABIN.