I have an Arctic Cat 366 ATV that had a faulty ignition switch. For the last few month I have had to wiggle the key around to make the machine turn on. It gradually got worse, until it would not work at all. I assumed that there was a bad electrical connection in the switch.
I removed the large plastic nut from the switch, unplugged it from the wiring harness and brought it to the workbench.
Before I took the switch apart I marked both pieces in case there was any confusion about how they go back together. I have found that a silver Sharpie works great for marking things like this.
When I pulled the switch apart the corrosion was obvious.
I used a small wire brush to scrub the corrosion off the copper contacts. Some of it was very hard and required a little scraping with a dental pick type of tool.
Before reassembling the parts I coated the contacts with a little silicone dielectric grease. This stuff is great for preventing corrosion, I put it on almost every electrical connection.
Once I reinstalled the switch the machine worked fine.