Connect the MS-2 2 button footswitch to your Mustang Amplifier for multi-function foot control. The utility menus allow you to assign one of the following functions to the 2 button footswitch: select presets (up/down), select quick access presets (QA1/QA2), bypass effects (various combinations), set TAP interval. For Mustang III, IV, V (note that the Mustang III should already come with the MS-2 foot switch. IV and V models do not.)