Noodling out the intermittent issues with a MacBook Pro wifi card
Suddenly, as I've read a lot of commentary on line, my wifi card in my MacBook Pro (2010) started working intermittently, at best. It was confounding...BUT....I found something that should help a lot of people.
I bought a used wi-fi card with the trouble started, used an Ifixit demo on how to replace it (piece of cake) and it worked great. For two weeks. Then, the same thing started.
So then I decided to buy a 'new' wi-fi' card, thinking the used one I bought was probably having the same issues. Installed the new one. It was even worse. Just got the big X in the toolbar wi-fi icon saying it wasn't installed. Now I was really flummoxed. Cleaned the pins on either end of the flexible power ribbon connecting the mother board (?) to the wi-fi card....nothing. No wi-fi, no bluetooth. Back to simply mac. I took the back off of the machine and just stared at it. Something to be seen here that is invisible to the eyes. I peeled the ribbon off very gently, looked at the antenna connections, and then I saw it! The tiny pins on the mother board end of the power ribbon had fallen off. It was lying there like a dead fly. Ah ha! Corrosion had gradually undermined the connections at that end, which explained the intermittent nature of the problem...but finally fell off. Off I went to the Mac Store. A friendly tech took one look at it and we started scheming. Surely there are some old parts we could salvage. He found a power ribbon from a 2012 that was being parted-out....it was half an inch short for me, but what the heck, I connected the ends anyway to see what I would get. Voila! I got blue tooth but no wi-fi because the housing couldn't be grounded with that ribbon. BUT, it was clear that power was now moving through the ribbon. I ordered a new ribbon from Ifixit, attached it carefully, put the back back on, and all the bars were lit up on my wi-fi. It wasn't the wi-fi card after all. It was the power ribbon, which is clearly the weak link in this scheme. How many people posted about trying to fix this problem, with increasing frustration, and never checked (or had a way to check) the continuity in the power ribbon. In my case, it was clearly only partially detatched, which was fooling me into thinking it was the wi-fi card. It wasn't until the pin assembly parted completely that the light went off.
If you start having wi-fi issues, the first thing to check continuity with a multimeter on the power ribbon. Or get a good loop so you can really inspect the connection where the pin assembly attaches to the ribbon. Start there...and only once you've determined that the ribbon is intact and functioning, turn to the wi-fi card. One thing they don't stress in the how-to videos is making %#*@ sure you get that wifi card installed correctly under the little tabs so that the entire card is properly grounded when the housing is screwed back into place. Makes all the difference. An ungrounded card will give you the same fits as a broken one.