The Infini I-501R rear light has an automatic mode and a manual mode, either can be set up steady or blinking. In automatic mode, the light senses motion and ambient light to turn on/off.
When the light is in automatic mode the button will flash green slowly.
In manual/regular mode the button will flash green quickly.
If the green light on the button stays on, the batteries are low and should be replaced.
To Switch Modes:
Tail light is off -- quick push of button --> tail light is on in automatic mode -- quick push of button --> tail light is in regular/manual mode -- quick push of button --> tail light turns off.
To switch the tail light from steady to flashing, you have to first turn the light on (one quick push of button to turn on in auto mode, two quick pushes for regular/manual mode). Once in the desired operation mode, push and hold button for 3 seconds and light will switch from steady to flashing (or flashing to steady). The tail light will turn on and off in whatever light pattern (steady or flashing) was last selected.
To Change the Batteries:
Find the notch where the lens and back of light meet. Use a flat object to pry the two halves apart. Replace the 2 AA batteries, ensuring they are inserted in the correct direction/polarity. Snap the two halves back together, making sure the lens is not upside down, as this will damage the electronics on the inside of the light.
TIP: Most often, when the light seems dead or does not work, new batteries are needed and/or the light is in automatic mode.
Here is the factory manual for the Infini rear tail light found on the Galaxy ST/TT and Delta X.