Loren,

I went throught the same process when I built mine. The ground in the middle position was a no-brainer. You can also get by without strictly observing polarity of those North American (forget the name) AC plugs...but what I did was to use my multimeter to make sure that the +/- plugs on the AC feed lined up consistenly (i.e.- the power cord feeding the back of the box had one larger blade -- I made sure that it matched up with the larger blade on the DC transformer that it was connecting to. Make sense? If not, give a yell and I will try to make this plainer). For $15 or so, you can get a basic polarity tester at Radio Shack or Home Depot but, assuming your house wiring is OK, it is probably simpler to just make sure that your plugs line up. Plus, I don't think that the DC transformer that comes with the Empeg cares about polarity, so it's probably not a big deal.

[Oh, the green is ground, white is +/hot and black is -/ground]

Clear as mud?