the light on my dcd800 stays on all the time even after i let go of the trigger, drains the battery.

Diagnosis

The issue with the DeWalt DCD800B LED remaining illuminated is typically caused by a failure in the trigger switch assembly or a "sticky" electronic state in the motor controller. In the 20V Max Brushless line, the LED is not a simple parallel circuit; it is managed by the tool's logic board. When you pull the trigger, the board sends power to the motor and the light; upon release, the board is programmed to hold the light for a few seconds before cutting power. If the light stays on indefinitely, it indicates that the control board still perceives a "closed" signal from the trigger switch. This is often caused by microscopic debris, such as drywall dust or metal shavings, infiltrating the trigger housing and physically preventing the switch from returning to its neutral position. Alternatively, it can be an electrical failure where the internal MOSFET or a capacitor on the control board has failed, creating a "leak" that keeps the LED circuit energized. You can confirm this by checking if the drill attempts to spin when you insert the battery; if the light is on but the motor is silent, the failure is isolated to the LED logic path of the trigger switch.

How to Fix It

Since this is usually a mechanical obstruction or a switch glitch, follow these steps to attempt a recovery before replacing parts:

1. Remove the 20V Max battery immediately to prevent the cells from deep-discharging, which can permanently damage the battery pack.
2. Use a can of compressed air or a high-pressure air nozzle. Insert the nozzle into the gap between the trigger and the plastic housing. Blast air repeatedly around the trigger pivot point and the rear of the switch assembly to clear any conductive dust or debris.
3. Perform a "Trigger Reset": With the battery removed, rapidly pull and release the trigger 20 to 30 times. This helps break any oxidation on the internal contacts or physically dislodges a stuck spring mechanism.
4. Inspect the trigger's physical travel. Press the trigger and ensure it snaps back instantly. If there is any "mushiness" or lag in the return, use a small amount of electronic-grade contact cleaner (such as DeoxIT) sprayed directly into the trigger gap.
5. Re-insert the battery. If the light stays on for the standard 5-10 seconds and then shuts off, the issue is resolved.

If That Didn't Work

• Replace the Trigger Switch Assembly: If the air and contact cleaner failed, the internal switch has likely suffered a mechanical failure. You will need to disassemble the DCD800B housing by removing the Torx screws. Locate the trigger assembly (Part # varies by region, but look for the trigger switch module). Unplug the wiring harness from the main PCB and install a new OEM trigger switch.
• Check for Housing Warp: In some cases, if the tool has been dropped, the plastic casing can pinch the trigger. Loosen the housing screws by a quarter-turn and see if the trigger regains full movement. If the light turns off, the housing was too tight, causing a constant "on" signal.
• Test with a Different Battery: While rare, a faulty battery communication pin can occasionally confuse the tool's logic board. Try a known-good 20V Max battery to ensure the "ghost" power isn't coming from a malfunctioning battery BMS (Battery Management System).
• PCB Inspection: Open the tool and inspect the main circuit board for "burnt" spots or leaking capacitors. If you see a scorched area near the LED output trace, the board has shorted and the entire electronic module must be replaced.

Heads Up

• Avoid using WD-40 or standard lubricants inside the trigger assembly; these attract dust and will eventually cause the switch to seize completely.
• Never leave the battery in the tool if the light is stuck on; a fully drained Li-ion battery can fall below the voltage threshold, rendering the battery pack unusable.
• Keep the tool away from magnetic debris (like steel wool or metal filings), as the DCD800B's vents allow particles to enter the trigger area easily.
• When replacing the trigger switch, ensure the wiring harness is seated fully and the locking clip clicks into place to avoid intermittent power loss during high-torque applications.