For a while, my turn indicator has been working kind of sporadically, then it quit altogether. Now, whenever the heater is on, it works fine, but as soon as the heater is off, it stops working?
I’m calling Monday to get it fixed, but does anyone have any idea why this is happening?
If it only works when the blower is running, probably a short or voltage bleed between the blower circuit and part of the turn signal circuit. If it only works when the mode switch is in the heat position and/or the temp switch on high heat, possibly a wire that is being caught and moved by an air door in the ductwork.
What Gary T said.
[hijack]One time a service advisor handed me a repair order with the following complaint “Turn signal works intermittently” I told the service advisor that is how they are supposed to work
It’s on
It’s off
It’s on again
It’s off again
He then explained that sometimes it did not work at all. 
[/hijack]
Any chance your heat is blowing on the flasher unit down on the fuse panel? Those things go bad and maybe the extra heat is what it needs to work.