Help with tstat wiring at control panel

[spd7171]

I was attempting to install a smart thermostat that came with a c wire adapter.  I thought I needed the adapter so I unhooked the wires at my control panel then noticed that there was a blue wire hooked up to to C wire spot.  Started putting wires back in and saw a loose black wire that I did not unhook.  The black wire at the thermostat was hooked up to a spot labeled W2.  I'm assuming it came unhooked when I was pulling the other wires out.  My only places to put it are marked AL1, AL2 or A.  This is a geothermal system with emergency heat strips.  Here is the wiring diagram.