my installation drill’s led worklight stays on all the time even after i release the trigger

Diagnosis

The Milwaukee M12 FUEL Installation Drill (2505-20) utilizes an electronic trigger system that manages both the motor speed and the LED worklight timing. When the light remains illuminated after the trigger is released, it indicates a failure in the "off-state" signal. This is typically caused by a mechanical failure in the trigger's internal spring-loaded contact or, more commonly, a failure of the MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) on the internal control PCB. If the MOSFET fails in a "closed" or "shorted" state, it creates a permanent bridge between the battery terminal and the LED circuit, bypassing the trigger's command to shut off. You can confirm this by checking if the light stays on even when the battery is barely seated; if the light flickers or stays solid without the trigger being touched, the fault is electrical rather than mechanical. Additionally, if you notice the tool is slightly warm to the touch near the handle even when idle, it confirms a parasitic draw caused by a shorted component on the board.

How to Fix It

To resolve this issue, follow these steps to attempt a mechanical reset and an electronic discharge before proceeding to component replacement:

1. Remove the M12 battery pack immediately to prevent deep-discharging the cells.
2. Perform a "Trigger Cycle": Rapidly pull and release the trigger 20 to 30 times in quick succession. This helps clear any metallic debris or carbon buildup from the internal micro-switches that may be physically jamming the contact in the "on" position.
3. Perform a Hard Reset: Leave the battery out for at least 60 minutes. This allows the capacitors on the control board to fully discharge, which can occasionally clear a "latched" logic state in the LED timer circuit.
4. Inspect the trigger gap: Use a flashlight to look into the trigger housing. Ensure no sawdust, drywall dust, or debris is lodged between the trigger blade and the tool casing, preventing the trigger from returning to its full neutral position.
5. Reinsert a fully charged battery and test the trigger. If the light remains on, the internal trigger switch assembly (Part # 452-XXXX series) or the main PCB requires replacement.

If That Didn't Work

If the basic resets fail, you are dealing with a hardware failure that requires deeper intervention:

• Replace the Trigger Switch Assembly: The most frequent culprit is the trigger module itself. Since the 2505-20 is a compact tool, the switch is integrated with the speed controller. You will need to disassemble the housing using a T10 Torx driver, disconnect the wiring harness from the PCB, and install a new OEM trigger assembly.
• Inspect the Wiring Harness: Check the thin gauge wires leading from the board to the LED. In high-vibration environments, the insulation can rub through, causing a short-to-voltage that keeps the light powered regardless of the switch state. If you see frayed wires, solder them and apply heat-shrink tubing.
• PCB Component Replacement: If you are skilled in micro-soldering, you can identify the shorted MOSFET on the board. However, for most users, replacing the entire control board is the only viable path to ensure the tool's safety and current-limiting features remain intact.
• Professional Service Center: Because the M12 FUEL line uses highly integrated electronics, a Milwaukee Authorized Service Center can use a diagnostic jig to determine if the fault is in the logic board or the switch without guessing and replacing multiple parts.

Heads Up

• Battery Drain: Never store the tool with the battery attached if the light is staying on. This parasitic draw can drop a battery below its minimum voltage threshold, potentially bricking the battery pack.
• Dust Intrusion: The 2505-20 is often used in dusty environments. Use compressed air to blow out the trigger housing monthly to prevent particulates from jamming the micro-switches.
• Warranty Check: Before opening the casing, check your purchase date. Opening the tool housing typically voids the manufacturer's warranty.
• Voltage Warning: Always ensure the battery is removed before touching the internal PCB to avoid accidental shorts that could permanently destroy the motor controller.