Rear left flasher light stuck on Y

[Dieseler]

89 SR5 the left rear blinker light stays on as well as the dash indicator it is not flashing but solid , when the left flasher is applied the the flash circuit cycles like normal Hmmmm.
Anyone know the route cause off the top of their head.

 

[Vicm]

check for corrosion in the light socket, ,
What happend when you use the 4way flasher?
That should give ypu a hint where the probelm is.

 

[KLF]

I would pull the tail light assembly out, they are not as waterproof as they could be. Water gets inside the connector and can short out the pins. See if disconnecting it solves the problem.