"Jumper for BLTouch" kills board?

[rprussell2004]

After installing a bltouch, jumpering this jumper killed the board. No sparks, no smoke, but no lights and no functionality either.

Removing the jumper - removing the BLTOUCH - does nothing. My system is dead.

What does this jumper do? Implication is it's necessary like a sensorless-homing endstop jumper. I wasn't expecting a system killer.

Where is the documentation?