This article walks through how to assign the SL 3's Aux, or third, deck to a MIDI controller.
First make sure you have the 3rd or 'Aux' deck enabled. To enable, go to the set up screen, click on the Plugins tab, and check the ‘Enable SL 3 AUX deck plugin.'
Now go back to the main screen and change the screen mode to Stack Mode:
This will display the 3rd deck on screen so you can MIDI assign it's functions; Pitch control, Cue points, loops etc.
Assign MIDI functions as per normal, by clicking on the MIDI button at the top of the main screen. Note: If you aren’t familiar with how to MIDI map a device in Scratch Live see: MIDI In Scratch Live 101
Other functions that don't have 'buttons' on screen can also be assigned by clicking on the "Show MIDI Panel" button (e.g. load to deck, library scroll etc.) Click on the AUX tab to assign these extra AUX deck functions to MIDI:
Once you have everything assigned, unclick the MIDI button, and away you go. If you wish, you can switch the view mode back to classic mode - the AUX deck MIDI assignments will still work behind the scenes.