If you are comfortable with surface mount components, here is a second method of implementing the HL2+ power switch connections. It has the advantage of the switch not handling HL2+ power supply current, it instead controls the enable pin of the HL2 3.3V regulator U3 as a means of turning the HL2+ on or off. See page 2 of the HL2 schematic for details.
To implement this method of HL2+ DC power control:
1. Remove J24 on the bottom of the HL2 PCB by DB9 6-pin header pads 5 and 6. See the second (rightmost) arrow on the Kicad graphic (which is an "X-ray" top view looking through the board).
2. Add a 10K ohm 0603 resistor to the previously empty R8 pads on the bottom of the HL2 board by DB9 6-pin header pads 4 and 5. See the first arrow on the Kicad graphic.
3. Install the included power switch harness 2-pin male header at DB9 pins 5 and 6. The header pins may be a little tight going into the through-holes in the HL2 board as they are spaced at slightly wider than the 0.100" spacing of the header pins.
4. Plug the included 2-wire harness for the power switch onto this header.
5. Solder the included 2-wire harness wires to the power switch.