Arduino not driving RGB LED Strip
From what I can see this little box is designed to take a 12V low-current signal and amplify it to a 12V high-current signal.

It is not suitable for directly connecting to an Arduino.

You will need three NPN transistors to connect between V+ and each of the R, G and B inputs, and then drive the bases of the transistors through a resistor from the Arduino.

But that's only a wild stab in the dark since there seems to be absolutely no documentation available anywhere.

After much hunting I managed to find this image:



so it seems it is designed to go midway through a chain of LEDs to power more of them, not be driven by a low voltage device like an Arduino.