Error code 3 on water softener and fried switch?

Well the funny thing is this. If they have the harness in stock as well as the switch. Then my guess is there was a problem with both. More than likely these are revised parts (upgrades) to correct a prior issue. There are only 3 things it could be 1 switch, 2 harness 3 motor. But your control board appears to be functional. If the switch was bad and arched itself myself I would probably replace the harness. But the parts guys should know what they send out the most. And that should be able to help you as to get it or not.