Fixing A Cordless Drill Trigger

Replace the trigger switch in a cordless drill

By the experts at The Family Handyman

From The Family Handyman

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If your cordless drill cuts on and off during use and then suddenly dies, the trigger switch may be suspect, especially if the drill is a variable-speed model that has seen heavy use. Repetitive switching between “forward” and “reverse” and running the drill between slow and max speeds have probably “fried” the switch’s movable contacts.

Triggers are fairly easy to replace. Look in your owner’s manual or the Yellow Pages under “Tools, Electric” for the nearest service center. If you visit a local service shop, either bring in the drill or check the make and model of your drill and take in the old switch to match the new part. If you don’t have a set of schematic drawings (with parts list) for your drill, get one at the service center.

“Regular duty” cordless drills have two-part switches consisting of the on-off switch wired to a separate forward-reverse switch. “Professional” and “best” grade homeowner drills have a one-piece, modular switch. Depending on the drill, a new switch should cost $20 to $35.

Begin the repair by removing the battery and then the drill casing screws (our drill had eight). Slowly open the drill case and carefully study the innards, comparing them with the drill’s schematic drawings and parts list (Photo 1).

NOTE: Acting in haste now may result in frustration and embarrassment later when you have to slink back to the repair center with a half-assembled drill in a grocery bag. When we opened our drill case, a “mystery part” ejected from somewhere in the drill assembly. If that happens to you, identify and properly reinstall those parts before proceeding.

Our drill’s schematic included a wiring diagram for the trigger. Remember, our drill has wiring and parts that may differ from yours. If necessary, before disconnecting the old switch, draw your own map (or take a Polaroid or digital photo) of the color-coded wires that run from the motor and the battery terminal into the “friction fit” connections in the bottom of the trigger switch housing. Once you’ve traced your drill’s wiring, remove the old switch.

Install the new trigger switch (as shown in Photo 2).

NOTE: Pull out each wire in the old switch and replace it with its exact counterpart in the new switch before proceeding to the next wire.

Before closing the drill case, use cotton swabs to clean dirt and excess oil from the motor and other parts (Photo 3).

As you slowly close the drill case, check to see that parts and wires aren’t slipping out of position in the assembly. In the same way you’d install the lug nuts to mount a car tire, first insert one casing screw near the bottom of the handle, then install one near the drill’s chuck. Secure these screws partway and insert the rest in the same opposing fashion. If the two halves nest together tightly without force, the wiring is probably not pinched; finish tightening all the casing screws.

Click image to enlarge.
1. Take out the battery, then remove the screws that join the halves of the case. Carefully remove parts and wiring from their positions in the drill case so you don’t jolt other parts loose. Before dissecting the tool, carefully study the general parts layout and wiring “pathways” inside the drill case. As you proceed, the key is to lay wires in their original places as parts are replaced and avoid pinching the wiring when later reassembling the drill case.

Click image to enlarge.
2. Remove the old trigger switch by first disconnecting the wiring harness from the heat sink. Lift the old trigger partially out of the drill case to access the wiring connections that run from the motor and battery terminal into the bottom of the trigger housing. Release the wires from the old switch by inserting thin or thick paper clips into the friction-fit connectors that hold them. Then insert each new wire for the new switch.

3. Clean any dust and old lubricant from both the inside of the drill case and the ventilation ports on the motor. After you install the new switch but before you close the drill, reinstall the battery and test the switch. If the drill doesn’t run, refer to your wiring diagrams until you make the proper connections.