Usually, the pin #1 of a ribbon is colored in red or blue. Never trust the ribbon cable color! And never trust a cable.
Always check twice the correct polarity and voltage before pluging your module!
An example of a 16 pin connector. The red wire is connected to pin #1 (small triangle on the connector)
AC Input. There’s no polarity to respect. Just remember: due to circuit design, the “GND” input pad is directly connected to the system ground.