Making a car difficult to steal

Here's something i did in high school as a prank on one of my friend's truck......
I made up a dummy coil wire out of some old spark plug wire ends and a piece of vacuum line about 6'' long. I replaced the original coil wire with this one at lunch time. It looked like the real thing so much that he had fits after school trying to start it. Along comes yours truely about an hour later to help him out. I hooked up my booster cables to his now dead battery to my '71 Dart 4 door, pretended to check out some things under the hood, wiggled some wires here and there and then replaced the coil wire with the original one when he wasn't looking, then i went inside and started it up. I have never seen someone so relieved and mad at the same time since. To this day he doesn't know how i got it going.
This works great if you have black spark plug wires, and would be a great theft deterrent too.
If you are reading this Glen, i'm sorry.
And it wasn't me that jammed a pine cone in your filler neck so it took you over 1/2 hour to fill your truck up.......honestly.
Tom.