First disconnect the battery, then carefully slide the keyboard ribbon cable clamp to release the ribbon cable. Once you have the cable out inspect for damage either on the contact surfaces or the edge of the ribbon is torn. If you are sure the cable is OK, then re-insert making sure you have squarely entered the connector. You might find a piece of electricians tape folded over to make a handle mounted on the cable can help in pulling it into place.
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Review Step26 in this guide: [https://www.ifixit.com/Guide/MacBook+Pro+15-Inch+Retina+Display+Mid+2012+Upper+Case+Assembly+Replacement/9736|MacBook Pro 15" Retina Display Mid 2012 Upper Case Assembly Replacement]
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Review Step26 in this guide: [guide|9736|MacBook Pro 15" Retina Display Mid 2012 Upper Case Assembly Replacement]
Give that a try and let us know what happens.
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=== Update (07/03/2017) ===
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Looking at your images the ribbon cable look OK and the logic board connector does as well. So the only thing I can think of is the pressure from the battery damaged the keyboard.
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I don't think the isopropyl alcohol in its self could have damaged something here. Besides the mid frame wall would have contained most of the fluid as you worked on getting the battery out. Next time you should use ethanol alcohol as it does a much better job breaking the bond.
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So now you'll need to decide if you want to take the easy way or the hard way... The easy way is just replace the uppercase. The hardware is taking the upper case out again and then remove the keyboard and just replace it.
First disconnect the battery, then carefully slide the keyboard ribbon cable clamp to release the ribbon cable. Once you have the cable out inspect for damage either on the contact surfaces or the edge of the ribbon is torn. If you are sure the cable is OK, then re-insert making sure you have squarely entered the connector. You might find a piece of electricians tape folded over to make a handle mounted on the cable can help in pulling it into place.
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Review Step26 in this guide: [https://www.ifixit.com/Guide/MacBook+Pro+15-Inch+Retina+Display+Mid+2012+Upper+Case+Assembly+Replacement/9736|MacBook Pro 15" Retina Display Mid 2012 Upper Case Assembly Replacement]
First disconnect the battery, then carefully slide the keyboard ribbon cable clamp to release the ribbon cable. Once you have the cable out inspect for damage either on the contact surfaces or the edge of the ribbon is torn. If you are sure the cable is OK, then re-insert making sure you have squarely entered the connector. You might find a piece of electricians tape folded over to make a handle mounted on the cable can help in pulling it into place.
Give that a try and let us know what happens.