If you are switching this normally, wire it with the + and - as labelled and control the switching via the black + line as usual.
Aux switching would obviously be some sort of extra option and you would have to know how the manufacturer planned that type of switching. My GUESS is that you could have a number of these individually switched as normal, and have a single master switch connected to all the "aux switch" inputs to turn them all on at once (wired to 12V positive side).
A guess, as I said. Some LED's can be sensitive and if you aren't supposed to put 12V+ to that aux switch it may not be a good thing. If you decide to try it out, VERY quickly apply + to that lead to see if you get a quick flash of light. Don't leave it connected to burn anything up just in case! Documentation, of course, is the best way to go.