Sounds like your switch accumulated enough resistance to overheat the wires, but not enough to blow the fuse.
I'm sorry if this offends you. But, electrically speaking, this makes no sense, as resistance impedes current flow, reducing it in the entire circuit. Current flow is inversely proportional to circuit resistance. If the switch contacts have increased resistance it will generate heat right at the site of the resistance, not infer it elsewhere in the current loop.
I do agree about your actual procedure for switch overhaul. But, the switch itself is unlikely to cause a wiring meltdown, unless internal bits have made contact with frame ground, and in that case bits are broken and not likely repairable. However, even in that scenario, the fuse between the keyswitch and the battery should part to protect the wiring from damage (assuming the main fuse hasn't been bridged and defeated from doing its function).
There is quite a lot the OP is not telling us about the malady. And, I predict he will get the equivalent value in return.
Hi TT, no offense taken.
He did say that the wires got toasty, under the tank.
Maybe I inferred at the switch.
It is a fact that a dirty overheating switch can/does melt wire insulation near/at the switch (source of heat) before blowing the fuse.
(determined by wire guage and length, fuse size, amp capacity and voltage of battery and resistance of switch or other offending load, as well as the melting point of the wire insulation).
Which makes perfect sense, electrically speaking, because heat is a result of resistance. Heat also accelerates corrosion which causes more resistance that causes more heat. We have all replaced melted, burnt,
toasted connectors on these old corroded machines.
