Turn signal switch LED failures

[papakb]

I've worked on converting vehicles to LED lighting for some time now and something strange that keeps popping up is the bulb in the turn signal switch is hot on the case and grounded on the tip of the bulb. This is irrelevant to an incandescent lamp but puts reverse power on an LED and they won't light when the turn signals are used. Recently in a HMMWV that shorted the turn signal wiring and killed the lights until the LED was pulled. Even though the flasher units in military vehicles are solid state, sometimes there isn't enough load on them to make them flash after converting to LEDs and a resistor is needed inline to add some additional load on the sysytem.