It controls fuel pump, fan, and A/C. I would carefully inspect the wires that connect into those three components and go from there. It is also possible that the burned up harness itself shorted out, in which case you probably will not be able to tell given the crispy-fried nature of the wiring.
In my experience (limited to a Ford Ranger that torched itself in my driveway), burned up wires happen when something grounds out to metal where it should not. So, you may be able to see where the wire grounded even if the wire itself is too burned to give you any useful information. Look for blue metal under the hood by where wires run.
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