my m18 fuel sawzall won't turn on at all, battery is charged and clicks in fine, nothing happens when i pull the trigger

Diagnosis

The total loss of power in the Milwaukee M18 Fuel Reciprocating Saw (Model 2821-20) typically indicates a complete break in the electrical circuit between the battery terminals and the brushless motor controller. Because this is a Fuel model, the tool utilizes an electronic control board that manages power delivery; if the trigger switch (Part #02-06-2821) fails or a wire has vibrated loose from a solder joint, the controller will never receive the "start" signal, resulting in a dead tool despite a fully charged battery. Another common root cause is "terminal creep" or carbon buildup on the battery contact pins. If the copper tabs inside the tool's battery port have been bent inward or are coated in a layer of oxidized debris from jobsite dust, they will fail to make a secure connection with the battery's positive and negative terminals. You can confirm this by checking if the tool "flickers" or activates momentarily when you apply firm pressure to the battery while pulling the trigger; if it does, the issue is mechanical contact rather than an electrical failure of the switch.

How to Fix It

If the tool is completely unresponsive, follow these steps to isolate and replace the faulty trigger assembly:

1. Remove the battery and all accessories. Use a T20 Torx driver to remove the housing screws located on the sides and bottom of the tool chassis.
2. Carefully split the two halves of the plastic housing. Be mindful of the trigger spring and the locking pin for the shoe; do not let these snap out of place.
3. Inspect the wiring harness connecting the trigger switch to the control board. Look for any pinched wires or loose spade connectors. If a wire is detached, solder it back to the terminal or crimp a new connector.
4. If the wiring is intact, remove the failed trigger switch assembly (Part #02-06-2821). This involves disconnecting the wiring harness and sliding the switch housing out of its molded slot.
5. Install the new trigger switch, ensuring the spring is seated correctly so the trigger returns to the neutral position automatically.
6. Reassemble the housing, tightening the T20 screws in a cross-pattern to ensure an even seal against dust and debris.
7. Insert a fully charged M18 High Output battery and test the trigger response.

If That Didn't Work

• Test the Battery Terminals: Use a fine-grit sandpaper or a cotton swab dipped in isopropyl alcohol to clean the copper contact pins inside the tool's battery bay. If the pins are bent, use a pair of needle-nose pliers to gently pull them back into alignment so they make flush contact with the battery.
• Inspect the Control Board: Examine the brushless controller for "magic smoke" signs—burnt capacitors or blackened circuit traces. If the board has shorted out due to overheating or a massive power surge, the entire electronic module must be replaced, as individual components on these boards are not serviceable.
• Check for Internal Shorts: Inspect the motor lead wires. In high-vibration tools like the 2821-20, the insulation on the wires leading to the motor can rub through against the metal chassis, causing a short that triggers a safety shutdown in the controller.
• Verify Battery Health: Even if the charger says the battery is full, the cells may be unbalanced. Test the saw with a different M18 battery, preferably a High Output (HO) pack, to rule out a "ghost charge" where the battery shows full voltage but cannot provide the amperage needed to engage the motor.

Heads Up

• Avoid using "contact cleaner" sprays that leave a residue; always use 90% isopropyl alcohol for cleaning battery terminals to prevent attracting more dust.
• When reassembling the tool, ensure the trigger spring is not twisted; a twisted spring can cause the trigger to stick or prevent the tool from shutting off.
• Periodically blow out the motor vents with compressed air. Sawdust buildup around the brushless controller can cause overheating, which prematurely degrades the electronic components of the trigger switch.
• Always remove the battery before opening the tool housing to prevent accidental activation or short-circuiting the control board during the repair process.