A while back, our garage door opener (a Genie Pro 82 screw-drive) developed an odd problem: the light was stuck on. Normally, it is supposed to turn off a few minutes after use, but now it stopped turning off.
I reasoned that it was probably a relay that failed (it's always the moving parts that fail) and that it was stuck in the closed (i.e. "on") position. A quick search online confirmed that this is a common failure mode.
The opened opener: