Shorting plugs are used to verify the quiet, hum free operation of your preamp without the turntable.
How to use them?
1. Turn down the volume on your amplifier
2. Have all devices powered off
3. Disconnect turntable cables from the phono preamp inputs
4. Disconnect the ground wire
5. Plug in the shorting plugs
6. Power up all devices
7. Slowing turn up the volume to normal levels
The result should be no hum