How can I install a .ipa file to my iPhone simulator

You can't. If it was downloaded via the iTunes store it was built for a different processor and won't work in the simulator.

I found an .ipa file that I wanted using iTunes and copied it over to my desktop.

After that I changed the extension to .zip and extracted it.

Next I found the Payload folder and moved the application inside to my desktop.

Finally I moved that application to my iPhone simulators applications folder found at:

• HD
• > Applications
• > Xcode.app (right click - Show Package Contents)
• > Contents
• > Developer
• > Platforms
• > iPhoneSimulator.platform
• > SDKs
• > iPhoneSimulator6.0.sdk
• > Applications

Hope this helps! (Note: Some apps crash more often than others.)

In Xcode 6+ and iOS8+ you can do the simple steps below

1. Paste .app file on desktop.

2. Open terminal and paste the commands below:

   cd desktop

   xcrun simctl install booted xyz.app

3. Open iPhone simulator and click on app and use

For versions below iOS 8, do the following simple steps.

Note: You'll want to make sure that your app is built for all architectures, the Simulator is x386 in the Build Settings and Build Active Architecture Only set to No.

1. Path: Library->Application Support->iPhone Simulator->7.1 (or another version if you need it)->Applications
2. Create a new folder with the name of the app
3. Go inside the folder and place the .app file here.