Step 4: Crimp the LEDs
Hold your 3 LEDs side-by-side, so that the 3 positive leads are parallel. Place a butt splice over all 3 positive leads. With your pliers, squeeze the butt splice where it encloses the 3 LED leads, being careful not to crimp the opposite site of the splice. Apply enough pressure so that the 3 leads are held solidly in place.
It's very important that you remember which are the positive LED leads; you may want to mark this splice with a small piece of tape. If you get confused, each LED lens has a little flat spot next to the negative lead. Now gather the negative leads, and place the other butt splice over all 3 leads. Again, give it a good squeeze, being careful only to crimp the LED side of the splice.