Sometimes we do mistakes. In a batch of SMD units I ordered from China there was a bad drawing of the circuit around the 12V to 5V regulator. The multiplexer was working fine when powered up through the USB cable but, if powered from the 12V/GND screw connectors, there was no 5V that the multiplexer needs to operate. Instead of throwing the units away, I removed the inductor of the switching regulator, made 2 holes on the PCB in order to pass a wire to deliver 12V to another switching regulator mounted underneath the PCB and to pass another wire to bring back 5V to the top layer of the PCB. The switching regulator mounted underneath the PCB is EXACTLY the switching regulator that I use on the TH (Trough Hole) units. The final result is a NMEA3WIFI multiplexer fully operational and tested by me. The components with the red X over them are doing nothing (I could desoldered them but left them there).
In the following picture you see the (TH) switching regulators mounted on the bottom side of the PCBs:
And in this picture you see the TH regulators when the PCB is screwed to the plastic box:
I will delete this topic when the units described here no longer exist. In the selling webpage of this forum you can see how you can buy one of these units.