Turnout Control Repair

For some reason we found that the roundhouse lead low-boy turnout indicator was showing both aspects when the turnout was in the divergent track mode. This should be impossible as a switch selects which output is active at the moment. The controller had an LED that did not work on the control panel in the box which we speculated might be shorted and feeding backwards causing the problem. We decided to replace the motor module that also contains the switch that controls which LED is lit and while we were at it replace the control panel module to fix the LED problem. After replacing the working parts of the turnout control we flipped the switch and now the LED worked but the low-boy still showed both of the aspects! Since it was the early design control box Tommy decided that maybe there was some wiring error in the box so he checked all wires and they were correct but one white wire which only involved the cutout circuit. I realized the low-boy had its B+ fed from the wrong place and we corrected that with a wire nut. We found we still had the low-boy problem. Next I suggested that maybe the LED was "leaking" in the box because if we disconnected the control panel LED the low-boy problem disappeared so I suggested adding a series diode to block the "leakage" through the LED and that worked! Apparently the Yellow LEDs used on the control panel have a peak inverse (breakdown) voltage (PIV) that we are exceeding. The supply B+ is about 16V and that apparently bumps the LED into its peak inverse voltage range!