Rig a back feed thru a bad relay or safety switch, leave the positive off, touch the ground and watch the sparks. If you don't know how to do that, I'll be more than happy to fill you in on the details.
This could be fun! How about a demonstration? It'd be kinda like an early 4th of July.
Reminds me of the time a screw came loose inside the starter on my 1958 Willys Station wagon and shorted the windings. I had been shopping at the Fleet Farm in Hudson, WI and when I went to start it to head home smoke started rolling out from under the hood! I quickly opened up the hood and saw the insulation on the positive cable from the battery to the solenoid melting off. I grabbed a wrench from my tool box but by the time I started to loosen the terminal clamp it quit smoking. I wrapped the cable with some duct tape to insulate it from shorting on anything else. I wasn't able to crank start it, but I was able to push start it, (fairly easy to do with that old thing, even by myself), and drive the ten miles or so home. Pulled the starter and found the loose screw welded to the windings. Took a week to get it back from being rebuilt and all was well.