The common cause seems to be a bad ground in the tail light assembly. I tried that fix, but it didn't help. I pulled the bulb that was intermittent and just lived with the warning light on for a while. I figured it was either wiring fault or a bad LKM. Things have gotten worse now. The dashboard backlight stays on all the time (even when the car is off) and if I turn the headlights on they strobe constantly, a couple times a second, as soon as I turn on the key.