I recently put back-up lights on my 03 Prarie 650 4x4 w/ a toggle switch. While I was doing the wiring, I had a mishap w/ the electrical tape coming off and the hot wire grounding out. I thought I caught it soon enough and pulled it off but now, since that happened, I have 1 of the pistons not firing. Why would a short from the battery/ toggle switch wire cause one of the pistons not to fire?

 

There are 2 ign coils, one for each cyl. Swap the coils and see if the problem (no firing) changes to another hole. Then, it's the coil. If not, it can be the igniter.

 

How can I tell which one is firing and which is not? It's hard to tell.

 

Actually just look at the grounded spark plugs when they are out of the cylinder heads and laying on the block or heads. If one isn't firing, swap the coils side for side like Hayashi said. This will tell you if you have a bad coil or not.