I'm currently using an iMac Pro and LG Ultrafine 5k display. I would like to temporarily disable/shut off the second monitor. I tried using the "DisableMonitor app" and "SwitchResX", but when I tried disabling my second monitor, both screens turn black.
I will appreciate your help.
After testing many applications and applescripts - This cannot be done easily or reliably. What can be done however is by using a remote power switch using a small remote control on the AC outlet of the monitor. These can be picked up very cheaply - example https://www.amazon.co.uk/TOP-MAX-Control-Wireless-Sockets-applicances/dp/B01KFJQPX6/ref=sr_1_4?ie=UTF8&qid=1515627122&sr=8-4&keywords=remote+control+ac+power
Another option is a network remote power switch but these involve a little more setting up, but then you could have a desktop shortcut to toggle the monitor's power.
Get a video display switch (also known as a KVM switch), and leave input 2 empty. Some switches are "smart" and only show active video feeds, and that's not what you want. Switches are cheap for VGA and DVI, but since this is a Thunderbolt display, I will spend a couple minutes looking for an example.
Edit: Wow. I've only seen this $400 example, and it's limited to 4K: IOGear Thunderbolt 2 KVM / Docking Station (GTD732)
