There are a number of things that will cause the ground to smoke and get hot.
The first is a dirty or faulty ground or ground wire. A short to ground will also cause this. Basically that is a faulty component that is supposed to "use up" the voltage but it is shorted internally and it does not use the voltage and so there is too much after the load and the wire gets hot.
If the blower was coming on even with the key off then I suspect you have a shorted relay which is what the control uses to turn the fan on and off.
To test this, we need to remove, test, and/or swap the relay with another.
https://www.2carpros.com/articles/how-to-check-an-electrical-relay-and-wiring-control-circuit
You have two relays, one for low and one for high. I would suggest testing each relay but this would be the likely thing that is causing this if you have moved the ground to the frame directly so it is unlikely to be loose or dirty.
Below are the wiring diagrams. Please let us know what you find with this. Thanks
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Sunday, June 6th, 2021 AT 3:23 PM