DIAGNOSIS The worklight circuit is stuck on due to a failed transistor on the controller board or, more commonly, moisture or conductive debris causing a short across the light's trigger contacts.
FIX Try a hard reset to clear any stuck electronic state.
- Remove the battery.
- Pull and release the trigger 10-15 times to discharge any capacitors.
- Reinstall the battery. If the light is now off, problem solved.
IF THAT DIDN'T WORK Internal contamination is likely. You'll need to open the drill housing and clean the main controller board around the area where the trigger wires connect, using isopropyl alcohol and a soft brush.
HEADS UP A constantly-on LED will drain the battery over several hours. Get in the habit of removing the battery after use until this is fixed to avoid a dead battery when you need the drill.