How to connect to the internet with arch for ARM on a raspberry pi 3 b+?

Question

I've tried everything people recommend. My new arch installation just won't connect. I'm running the most recent image for the rpi 2 on an rpi 3 b+ because there is no explicit 3 b+ image. I've tried both eth0 and wlan0 interfaces with wifi-menu, wpa supplicant, dhcpcd, and systemctl. Nothing works, and I can't even ping my router. Furthermore, for some reason it was able to connect automatically when I was running raspbian on a different SD card. I then tried the arch one and it didn't work, of course. I went back to raspbian and it (connecting to the internet) had stopped working.