The spade terminals on the Ign Sw are metal and plated thinly.
As moisture and vibration as well as electrical conductivity begin to erode the plating, the terminal rusts and looses good contact.
Poor contact causes mini arching, and more rust forms, and so on.
Pretty quick the heat produced from arcing begins to melt the plastic connector holder.
Just like a small snowball grows as it continues down hill.
There is not a large current draw causing the problem.
It is a corrosion problem compounding itself.
Add to that, usage in a moist environment either from high humidity, and or outside conditions and you have a failure of the connections.
You can purchase individual female spades and the plastic molded holder/connector on Epay if you so choose.
