Chosen Solution
I got a MBP late 2011 with an unresponsive trackpad. Thought that I could fix this replacing the trackpad. But with the new (and definitely functional) trackpad the MBP refused to boot. Disconnecting the trackpad everything was fine (except the trackpad of course). I tried another trackpad just to make sure it was not the problem, same result. Any good hint to solve this? Update (11/26/2017) Thank you for your suggestions. Being busy with other things I only came back to the MBP today with some more testing. Looking at the logic board connector I could not find any damage. For further testing I left the trackpad untouched and just changed the connector cable. With the “original” cable the trackpad does not work, everything else is fine. Substituting the cable for one which definitely works, the MBP cannot be switched on any longer, the attempt to do so gives only a short signal, but the machine cannot be turned on. This is true regardless whether de cable is connected to the trackpad or not. Remove the cable from the logic board and everything (apart from the trackpad of course) works just fine. The AHT does not report any problems. Any more hints? Thank´s in advance.
Using a magnifier do a detailed inspection of the logic board connector. I suspect you have a damaged pin. Post a few pics if you see something off. Update (11/28/2017) Well, the logic board connector looks OK which what I had expected would have had a damaged contact. Clearly it’s not that. So what is it?? At this point I’m thinking you have either a defective trackpad or the wrong one for this series. Make sure you got the right one.
Before you rip apart your laptop, check to see if it was disabled in settings. Go to System Preferences > Accessibility > Mouse and Trackpad If that doesn’t work, internally restart it by pressing the Shift-Control-Option Keys and the Power Button all at once, then release. Good luck! EDIT: Make sure to shut down your laptop, plug in the power cable, and then restart it before attempting the last fix.
