Help. My truck

That fuse feeds the front running lights too. Use a pair of spade terminals and jumper wires to replace the fuse with a 12 volt light bulb. The bulb will be full brightness when the short is in the circuit, and it will dim when you do something to remove the short such as unplugging a connector or moving a wiring harness. When the short is gone, there will be a lot of bulbs asking for current so the test bulb will still be fairly bright. In that case using a headlamp bulb will be easier to notice. For lower current circuits a brake light bulb works well.

It's possible. Some designs have a contact that grounds a circuit to turn it on rather than apply 12 volts to it. If part of the switch isn't working, such as a contact not sliding to its proper position, it could be touching that grounded contact or even the switch housing. That would be rare though. I'd suspect a wiring problem first.