The fact that you want to use a car relay to switch 110vac tells me you have no business leaving devices you've built/modified with that have heating elements unattended. If you know enough to do it well, you won't need to ask for help. If you don't know enough to do it well, you shouldn't be doing it.

Discussions regarding modifications that allow unattended operation will not be permitted here. Topic closed.

Anyway. #1 Sensor beams thru the hopper at its base (hopper would need to be redesigned to accommodate for sensor or drilled to make fit it in)
Once #2 sensor detects #1 sensor, 15 amp car relay would trigger and disconnect 110v.

I have this relay on my Robo3D printer. When print is done, M81 code triggets 5V relay. 5V relay triggers 12V relay that passes 110V, thus shutting down entire printer. It works great i posted on Robo3D forum and use it almost daily before i leave to work.

It would be nice to have something like that for a filastruder. A 12V relay would be very simple solution. The only thing i need to figure out is what sensors to use and how they gonna work. I have 0 knowledge about sensors and how to use them.

Please help.
Maybe simple blueprint that everybody could understand ?

Thanks !