This is an adapter that I use to breakout +3v, +5v, and +12v from a pc power supply as well as monitor voltage and amperage. Basically a cheap lab bench power supply.
The ground for each voltage goes through a shunt which is connected to the dial. The commons for the dial are connected to the amperage and voltage leads on the display. The standby light is connected to the +5vsb(pin 9), the status to pwr_ok(pin 8) and the switch shorts ground and pwr_on(pin 14). There is also a 10w ceramic resistor between +5v and ground to stabilize the power suppy when there is a low load. This is also why there is a fan in the case as the resistor gets very hot.