OK - but I don't see how I am screwing with the M4 by setting one DIP switch and trying both polarity settings on the on/off switch.
Anyhow, there is only one USB device connected; the touch USB for the screen. For sure, I am not disconnecting that to get the PS to work. No keyboard. No mouse.
Since the M2 I have removed all the USB devices (CANBUS, Radio, GPS, Mic, Bluetooth & FusionBrain) except for the touchscreen.