After upgraded to iTunes 12, none of devices (iPhone 6 plus, iPhone 5, iPhone 4s, iPad, iPod) are recognized. Connections are good. iMac won’t allow users to delete iTunes to reinstall.
Fix 1:- iTunes 18.104.22.168 update have bug fixes for this issue. So install the latest iTunes update to fix the issue.
Fix 2:- Shutdown both Mac and iPhone and restart the devices.
Fix 3:- Open Terminal app and type the following command
sudo killall usbmuxd
Kill the usbmuxd process using Activity monitor. iTunes will restart and detect your Apple device.
Fix 4:- Repair the Disk permissions using Disk utility and restart the MacBook Pro or MacBook Air.
Fix 5:- Uninstall iTunes 12 and all the programs associated (iTunes, Apple Mobile Device Support and Apple Application Support) and reinstall iTunes.
Suggest your own solutions via comment.