Can someone tell me why a household light switch would be added to the eletrical system of a 92 cherokee? The switch is near the battery and is grounded to the fender. The other end goes to the wiring harness that runs between the rear of the engine and the firewall. I've turned the switch on and off, and tried to start it both ways and the vehicle always starts. It's not a problem, I'm just curious. I just bought the jeep from my sister who only had it for a few months herself. I've asked her to try to contact the original owner and ask them, but she's having a hard time loctating them.

Because someone really has no clue, or really wanted to mess with you. jk.
You'd be best off if you traced it to the end and find out what the things doing there.
There's a reason there are different switches for cars and houses.

No telling....just take it out since it is a grounding switch anyway.