What was found
WHILE C/W LEARJET SB 35/36-52-10 (UPPER CABIN DOOR TORSION BAR ARM ASSEMBLIES); IT WAS FOUND THAT THE SHEATHING AND ALL THE WIRES INSIDE IT WERE BROKEN. THESE WIRES ARE FOR THE UPPER DOOR LATCH PIN SWITCHES. ACCORDING TO CHAPTER 52-10-10, PAGE 3 OF THE LEARJET 35 WIRING MANUAL, THESE SWITCHES GIVE A GROUND TO THE DOOR UNSAFE LIGHT. WITH THESE WIRES BROKEN, THERE WOULD BE NO LIGHT EVEN WITH THE 2 CENTER LATCH PINS NOT LATCHED. THIS FAILURE WAS CAUSED BY REPETITIVE CABIN DOOR OPENING AND CLOSING.