Hi pwd,
For me this generally this happens when...
1) Your communication cable is not properly plugged into the 5 pin harness connector.
2) Battery is not powering up the controller.
Tried to look into this further by trying to jump some connections and seeing the results. But it's so tight, just could do two at a time...
Error also shows when the below inputs are connected.
1) JUST 5 volt regulated power and battery ground.
2) JUST TX and RX.
3) JUST Battery + and battery ground are. Used my Smart Display for this one, shows communication error. Error 9.
Looking back on your controllers history, it may have been damaged by your direct shorting of the 5 volt regulated power during the brake switch wiring problem...?
Did you lose communication after this?
I would check for power at the controller communication 5 pin connector.
Pins 2 to 4 for 5 volt, 2 and 5 for battery. Hopefully something will show. Last hope would be continuity between controller board and TX RX pins...with no shorts.