greyed out wifi button in iPhone 6plus
Suddenly my wifi was getting connected and disconnected automatically and then i cant able to enable my wifi and its been showing some grey color above wifi icon
If the Wi-Fi signal is weak, it may be the antenna getting disconnected, or being broken.
If the Wi-Fi option is greyed out, it is a totally different story. The Wi-Fi circuit is damaged. That means the Wi-Fi chip is bad, missing a power line or an enable line; and/or some other components that are also part of that Wi-Fi circuit may have gone bad.
Troubleshooting and replacing Wi-Fi related component is hardly a DYI repair. It requires experience, skill, proper tools, and a good understanding of the Wi-Fi circuit.
This failure can happen after a drop (Wi-Fi chip is damaged, a pad is cracked, a line goes missing), prior board repair (heat harms the Wi-Fi chip or a pad underneath it), or spontaneously without apparent cause (for example, Wi-Fi chip dies).
Did you open your phone at all? Or did this happen out of nowhere? If you opened it recently, one of the antennae that @alwayslearning mentioned may have not been reconnected properly. It's also possible that your antenna just failed on its own, in which case I'd recommend following this guide to replace the antenna which is only $8. You can also try just reseating your antenna without swapping out a new one and see if that helps. Please let us know your results!
after lifting the lens assembly, on the top left inside the device are a couple of antennas that have the potential to be replaced and solve your issue.