[mrein3]

Years ago I converted my heat only truck to a factory AC system.
While collecting parts in yards and from used suppliers, I found that ALL the used plugs on the back of ALL the used fan switches were in various states of meltedness (new word - meltedness).

In the end I decided to simply order a new switch (still available from GM) and a new plastic plug for the back of the switch. I then bought correct gauge and color wire and rewired the whole harness. My thinking was the melting came from 40 or so year old wiring getting furry and losing conductivity.

Fast forward to this past spring. My new switch started acting wonky. I took a look at the plug and it was melted again.

I ordered another new switch and plug and put it back together with the intention of jumping up a size in the wire.

Long story short, don't go blaming anybody about your wiring. I'm starting to wonder if those resistors in the resistor block get too hot then transfer that heat back down the wire. I'm tempted to jump up a size in wire but that might not be the correct solution.

What happens in that resistor block is that the resistor drops the voltage down to 3 and 6 or 6 and 9 volts (I can't remember the exact numbers but I measured them the first time I rebuilt it). The lower voltage simply spins the fan motor slower. The rest of your 12+ volts gets turned in to heat which ends up wrecking your plug and switch.

In a perfect world a guy would design a circuit that does the same thing without those big resistors under there generating heat. Sounds like a future project.