More thinking, planning, labeling and double checking the wiring. This is my first time wiring a series of devices that communicate via serial ports and I want to reduce the risk of mis-wires.
BTW - I did find a wiring (or, labeling) error in a harness made by the fine folks at Aircraft Spruce. So it can happen and I recommend double checking everything - even the items you paid others to assemble.
Also, fired up the EFIS and EIS for the first time. No smoke!!