After configuring a new Raspberry Pi Zero W, I have not been able to ssh into it over WiFi. The IP address is assigned and pingable, but I get 'connection refused' errors.

After some research, I discovered one possible solution is to replace the SSH host keys on the pi.

But it's a Catch-22, because I can't login to the pi to change the keys that I need to change to be able to log into the pi. 

What can I do?

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*Why do I need to replace host keys?*

*Short answer: I don't know. I don't even know if that's the only or best solution or just one workaround.  Currently I'm wondering about a few things: The implications of installing Raspian full on headless Pis, also whether or not openssh got configured. One thing I did on both Pi's was added a dt overlay line in config.txt to enable ethernet over USB. Could have thwarted the boot/initialization sequence? Will run some experiments and post info if I learn anything new.*

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___Configuration details___: The way I configured my Pi's are as follows: Using __Etcher.app__ on __macOS__, I flashed an SSD card with the ___full___ desktop version of Raspian, `2018-11-13-raspbian-stretch-full.img`, downloaded from the Raspian site, and installed it on a __Pi Zero W__ and a __Pi 3B+__, both headless, and used the *headless* approach to configuring WiFi and ssh (i.e. touched `ssh` in /boot and created `wpa_supplicant.conf` in /boot).  

I didn't have this problem when I similarly installed Raspian ___lite___ (on my Pi 3B, about a month ago, `2018-10-09-raspbian-stretch-lite.img` 

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_Follow-up to @Milliway's comment below_: This is the Reddit thread containing post that gave me the idea that regenerating host keys might fix the problem:

https://www.reddit.com/r/raspberry_pi/comments/704v5y/ssh_connection_refused_off_a_headless_setup/