Transformers do not have input and output. You decide that. They work both ways. You need to discover voltage rating and current rating and turns ratios. The best way to do this is by measuring inductance of windings (although you'll have a 50/50 chance) not resistance. Why? because one side can be rated for much lower current and have a much higher resistance even though the number of turns might be smaller.
And if your transformer gets hot, you might be running the core into saturation. I dont know what a stun gun involves but if it uses high frequencies, you'll need a core that can handle it without running into saturation. If your project doesnt work at first and if the transformer feels warm, check this.