Chosen Solution
Any answers to this? Apple replaced my logic board back in Feb of 2017 including the I/O cable as well.
I would start off replacing the MacBook Pro 15" Retina (Mid 2012-Early 2013) I/O Board Cable as these often go bad. Follow this IFIXIT guide: MacBook Pro 15" Retina Display Mid 2012 I/O Board Cable Replacement. Next I would replace the MacBook Pro 15" Retina (Mid 2012-Early 2013) Right I/O Board. Follow this guide: MacBook Pro 15" Retina Display Mid 2012 I/O Board Replacement. If neither altered anything then the main logic board I/O cable connector is bad.
