Can someone help. I have a 2001 F150 and the left turn light will not flash with the park lights on. If I turn off the park lights then it will start to flash. Also the brake light that is on the back of the cab is on all the time except when I turn on the left turn signal it goes out. The right turn works fine so it appears there is a short somewhere. Need help I don't know where to look.
Thanks for the help.

 

My first guess is a poor ground that is used by more than one light in the wire harness.
Where you find it is the ? until a look see is done.

 

Thanks Bluegrass

I did find the problem. It was a short in the trailer light pigtail under the rear bumper. It had a lot of moisture and ice packed inside it.

Thanks for your reply. I forgot to log back in and let you all know it was fixed.

Thanks again.