When I turn my knob to make my dash lights come on for some reason it makes my back left turn signal stop working but if I turn car off take key out an start car again an leave dash light knob off the turn signal works but if I go to turn dash lights back on it stops again
Your car has a multi-function switch under the steering wheel for turn signals, cruise, hi/lo beam, wipers, etc. There is a ton of functions that runs through it.
I once had a multi-function, switch similar to this, cause my tail lights and turn signals to go crazy even though the exterior lighting switch was on the dash. So, it is possible this switch is malfunctioning.
Troubleshooting these is not easy. Replacing them is not for the beginner. You may want to consider taking it to a professional.