DeWalt DCD778 drill cuts out on full power

Hi Michael,

According to the specs your drill has a variable speed trigger, meaning the further you pull the trigger, the faster the drill spins.

That generally means there's a rheostat AKA potentiometer AKA variable resistor built into the trigger mechanism that provides a different resistance at different points in the trigger's travel. My guess here is that the potentiometer has either developed some corrosion or has just plain worn out at the point near the maximum trigger pull.

Unfortunately, it appears from the parts diagrams that the only way to get a new trigger is to buy the entire trigger/motor assembly like this one, labelled as part #2.

My suggestion would be to first try and take it apart and clean it. Get yourself some electronics component cleaner spray from the auto parts store and take the drill apart to where you can get to the trigger mechanism. This guide shows you how.

Dewalt DCD778 Motor Replacement - iFixit Repair Guide

Spray that mechanism down good while operating the trigger; you're hoping the spray will dissolve any corrosion or gunk that's gotten into the trigger and operating it will wipe it away. After that reassemble and test. If that doesn't do the job, you may need to replace the whole shootin' match, which ain't cheap. The most inexpensive one I saw was on AliExpress.

DC 18V 20V 18 teeth Motor and Switch N493868 Replace For N806546 Dewalt DCD777 DCD778 DCD7771D2 - AliExpress

Note that according to the listing, the DCD777 uses the same assembly. They do list a switch only assembly for the DCD776, but I have no idea if it will work in your 778 or not.

Switch For DEWALT N868644 DCD776 DCD776C2 TYPE1 CORDLESS DRILL PARTS - AliExpress

Hopefully that'll get you going; let us know how it turns out!