PTC Fuse?

there is an empty spot in my fuse box labeled ptc. What is this fuse for? If you look at it from the back side of the fuse panel it has a pretty heavy gauge wire coming in. I ask what it is for because i used the hot side of it as a 12v ignition source for my electric fan. But the issue is when the fan is running, and i turn the key to the off position, the truck doesnt die right away. Like its feeding back into the ignition system. The truck does shut off eventually, just seems kinda strange. Not really a big deal or anything. I already disconnected the fan from that point.

It's for the heater/deicer under the stock carb. If you swapped ou the OEM carb you don't need it - unless you are in a cold climate.

As for your other issue... maybe the fuel is not cutting off or dieseling.