Why all of a sudden furnace quits running and flashes yellow light reversed polarity. Nothing has been done to it.

I would try turning off breaker, turn on after maybe 10? Seconds? May be Confused

If cutting the power to reset the system doesn't work, look for loose wires, bad connections and examine the mother board carefully for burn marks, or scorches. Shorts or bad grounding is the first condition to examine.

Before messing around with wiring TURN OFF THE POWER. You can always restore the power safely afterward, so why fry yourself...or worse!