Today I wired up a HomeBrew AUX Relay using a pair of Gen3a PCBs. Here's what it looks like, next to one I had previously wired up with the earlier/larger Gen3 PCBs:
As usual, it took me two tries to get my head around which wires go where between the two boards. There are only four of them: Rx,Tx,BusyIn,BusyOut, but my brain gets twisted trying to put them in the right places. If I ever do another production run of PCBs, they'll have extra silk-screen labels to make that easier for me! 
Actually, there are seven wires in all, not just the four above. The other three are +12V, +5V, and GND. Those are easier to get right! 
After I finally got it wired correctly, it still took another hour for me to get the Relay working. Wait a minute.. been there before.. same issue with the first one I built.. Doh! Forgot (again!) to hardwire RX/TX together at the RJ12 jack on the Relay side, just like the mount itself does on the primary side of the Relay.
Must remember that next time..
I also wired up the Mount-USB selection switch, forgetting that this has no use on a Relay -- not enough hardware serial ports on the ESP32 for Mount-USB to work in this scenario. So.. it has an extra switch on it, which I may use to select "testing mode" or something. New source code will be released shortly, also fixing the build for when GPS_ENABLED=false.
Edited by mlord, 02 January 2023 - 10:59 AM.