Pilot DAR, you made me think about this, always assumed it was more sophisticated than just a light on the starter side of the solenoid, but perhaps it isnt. I always thought it worked on back emf from the starter acting as a generator because the likely mode of failure is failure of the bendix to retract but actully its just as likely that the solenoid could stick. I would say that it probaby does work to indicate both modes of failure actually and is thus ingeneous in its simplicity,