The signal light does not turn off.
The combination lights in the rear are known to take on water, due to defective seals. This could short the light socket, and a light may stay on. I recommend having a mechanic, like one from YourMechanic, inspect your turn signal lights to see if water has been, or is currently in, the lights and is shorting the sockets out.
Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing