As I covered here, Nikola Sizgorich gave us a very interesting tour around the Macy's (Wanakaker's) light show the day after Christmas. Mr. Sizgorich works with the Friends of the Wanamaker Organ, and he also gave us an amazing tour of the historic Wanamaker organ as well.
The organ keys are actually electrical switches, which terminate in a number of panels in the various chambers (see the site above for more details):
These then run electrically-controlled pneumatic valves, which then actuate small valves (which have a special name which I forgot) made out of leather (these are in the shop):
Air for the organ is supplied by massive blowers:
And this all feeds the 28,500 pipes (the pipes visible from the store are fakes):
Many of these areas are only accessible by now disused but beautiful areas of the building:
More photos here. Thanks again to Mr. Sizgorich for the amazing tour!