Help identify Rx Tx on NVR (all 3 pins have +3.3V)

[XrayZ]

Dahua NVR `2020 41хх series
Help identify Rx Tx on NVR (all 3 pins have +3.3V), ground found
Probably left two are Rx Tx ?

 

[Aquaman]

Temporarily touch something like a 1K resistor to ground on each of the pins one by one and measure the voltage. The Rx input pin will usually be the one that drops

 

[alastairstevenson]

Temporarily touch something like a 1K resistor to ground on each of the pins one by one and measure the voltage. The Rx input pin will usually be the one that drops

That's a good suggestion.
And if you don't have a 1k resistor, hold ground with one finger, moisten another finger and hold something conductive like a paper clip, touch it to the pins in sequence whilst measuring the voltage.
The RX pin has an internal pullup to 3.3v which can be dragged down a bit with a modest load.