Sorry, I was talking to Joe Muchel. Gets a bit confusing!
My advice remains unmodified if the issue occurs only when turning to crank position. This switch position does not overheat the switch since a) it is only a relay being switched (low current) and it is only for a few seconds. We have to be logical or we go round in circles. I have an S2 with a crappy spring as you describe and the previous one was iffy also, after 40 years. I know what you mean. Who knows, you might be right on the money, but typical switch burnout happens after hours of passing high current, not just clicking a relay. Listening for the relay itself is part of the diagnosis too of course, but for now we're just trying to keep the smoke in.
Either way, after two wiring fries on cranking (and failure to start) Joe absolutely needs to fit a fat earth to his engine, temporary or otherwise,to rule this in or out. It cannot do harm, only good, or nothing.
Pete