From: http://www.apple.com/ios/features.html#pcfree
"Wirelessly sync your iOS device to your Mac or PC over a shared Wi-Fi connection. Every time you connect your iOS device to a power source (say, overnight for charging), it automatically syncs and backs up any new content to iTunes. So you always have your movies, TV shows, home videos, and photo albums everywhere you want them."
Thanks for the tips. I was able to fix the problem of automatic Wi-Fi syncing not starting when connecting my iPhone (iOS 6.1.3) to a wall power adapter by doing the following:
Connect iPhone to computer with iTunes via USB
Select the iOS device and click the 'Summary' tab
Uncheck 'Sync with this iPhone over Wi-Fi'
Sync
Check ''Sync with this iPhone over Wi-Fi''
Sync
Unplug the iPhone from the computer USB cable and connect it to a wall charger adapter
Automatic Wi-Fi syncing should start now
As other people suggested, make sure "Prevent iPods, iPhones, and iPads from syncing automatically" is NOT checked (On a Mac, go to the iTunes menu -> Preferences -> Devices. On a PC, go to Edit -> Settings -> Devices)
No, this doesn't work!
Did these steps exactly and no change. Can synch manually, won't synch over wifi. Prevent iPods...from syncing automatically is not checked.
I plug the iPhone (6.1.3) into the wall charger and it never shows up in iTunes. Although from the iPhone if I go General, iTunes Wi-Fi Sync it sees the Mac.
I Googled and Googled and followed all the various suggestions to no avail. Finally, it occurred to me that maybe there was a problem with the trust relationship. This is what solved the problem for me:
https://support.apple.com/en-us/HT203887
So easy!
WiFi sync has never worked automatically for me. I'm not sure that it's supposed to. I always initiate the sync from the host Mac. After figuring out the above solution, if I'm still unable to see the target iOS device from the host Mac, then I simply have to make sure the iOS device is awake. For example, I have an old iPhone that I use as an iPod in my car. It falls asleep when the car is off. I usually open the door to my car to tickle the power to my iOS device. Then I go back to my Mac and sync.
I hope that helps.