The most common failure is an open circuit- - - -no current flow. A ballast resistor is just a coil of nickel/chrome wire, usually mounted in a ceramic heat isolator.
Jerry


"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!