If you don’t connect the com- terminal to the minus of your power supply then your outputs will slightly glow when off.

Improperly connected commons on sinking and sourcing PLC output transistors can cause voltage to “leak” by. Sourcing PLC outputs require a connection to both the +24VDC and the 0V of your power supply. If you do not connect the 0V, then the PLC output will slightly glow due to leakage current.

Let’s take a few minutes to understand why and figure out how to fix this.