[McMurphy]

You can Sherlock this if you have a voltsmeter.

You can hook it up to your ignition switch wire by wire and deduce what function they provide...

Somethings are a certain given though, like the red 1 wire will be a constant hot right off the battery or a junction like I installed in my build.

One will be to your starter when the key is turned to start.

The orange wire (either 3 or 4, I cannot tell in the photo) should be ignition ON/Running.

Then one of those will be Aux.

I forget what the blue one, and your empty slot would be for, sorry....
I hope this helps.