DIAGNOSIS A failed MOSFET on the controller board is stuck in the 'on' state. It's a known component failure.
FIX This is not user-serviceable. The entire controller board must be replaced at an authorized Milwaukee service center.
IF THAT DIDN'T WORK N/A. The board is the only component controlling the LED circuit.
HEADS UP The constant drain will kill a battery in days. Store the tool without a battery installed until repaired.