The digitizer cable is located towards the bottom left corner of the iPad about 2 inches up. Even though you'll be removing it and replacing it, still take care not to push it too hard as it can push into the LCD and damage it or pull up on components underneath the LCD. It's best to work around it.
This is the most difficult part of performing an iPad 4 or new iPad screen replacement as the screen is held in with nothing but adhesive. We are going to have to heat it up to soften the adhesive and slowly remove it with our iPad 4 opening tool. Make sure you perform this step extremely carefully and take your time. Before peeling off the backing to the adhesive, now is a perfect time to test the assembly instead of waiting until you've stuck down the screen with adhesive before realizing it's defective. Gently flip over the digitizer and power on the iPad 4. Once the slide to unlock screen comes up, go ahead and slide your finger to unlock to make sure the screen responds to touch. Tab through the Home screens for a minute to make sure everything is working like normal.
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