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
I suspect you have a bad earth in your rear light cluster. The likelihood is that the tail light bulb is leaking voltage into the earth pin of the turn signal so when the system applies voltage to the turn signal bulb, it doesn't actually make a circuit.
This type of fault is usually due to one of two things:
1) a poor or loose earth connection - check all the earth points and cables for the rear lamps,
2) an incorrect connection between the two circuits - damaged cables or even a faulty bulb... check all the cables for damage...
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.