It's hard to describe, but I'll try.
If you're looking at the left side of the mechbox
- put the mechbox in the receiver
- put the flora pin in
- put the stock pipe screw in finger tight
- put the grip on...screws finger tight
- take the wires that are going to lead to the battery and route them straight up the side of mechbox...get them out of the way of the bolt release/mag release area "under" the mechbox
- put the bolt release back in, put the mag release back in
- run the wires forward to the upper, without pulling them in such a way that they bind up on the bolt release "leg/lever" or the mag release.
Anyways...you'll see if you've got them all wonky...the operation of the bolt button and/or the mag release will seem to rub/catch on something...and/or mags won't seat properly.
Good luck. Don't rush