A few years ago we had a very similar situation to the one mentioned. We have two cars and only one was suffering from this intermittent problem. On an off weekend of racing we went to the local track to practice/troubleshhot. We would trade parts off of the good running car onto the the popping car to try to find the problem. Bottom line of this whole deal is the on and off switch. After we switched it, which by the way, was no where near the first handful of items switched, the problem went directly over to the other car- only.
When we returned home I opened up the bad switch and found a whole bunch of some sort of watery gook. I also checked the other switch and it also had a little bit of moisture inside of it.
I hope this helps some, now I just change the switches out every three to four months. This problem has not come back again.
I have tried high dollar switches, mid range, covered, and hell I even went as far as to try to seal a switch with silicone on the outside to keep out moisture without luck,they all seem to get wet internally and start playing tricks on the electrical system.
