To link a 3W LED step light with a DMX512 controller, you will need to follow these steps:

1. Connect the DMX512 controller: Connect the DMX512 controller to your DMX512 system or network. The DMX512 controller typically has an input and output port for the DMX512 signal. Connect the DMX512 input port of the controller to the DMX512 output port of your DMX512 system or network.

2. Connect the LED step light: Connect the 3W LED step light to the DMX512 controller. Typically, the LED step light will have an input port for the DMX512 signal. Connect the DMX512 output port of the controller to the DMX512 input port of the LED step light.

3. Set the DMX512 address: Set the DMX512 address of the LED step light on the DMX512 controller. The DMX512 address determines the channel or channels that the LED step light responds to on the DMX512 network. Follow the manufacturer's instructions for setting the DMX512 address on the controller.

4. Configure the DMX512 channels: Configure the DMX512 channels on the DMX512 controller to control the various functions of the LED step light, such as color, intensity, and effects. For a 3W LED step light, you will need to use a single DMX512 channel. The DMX512 channel value will determine the brightness level of the LED step light.

5. Test the DMX512 control: Test the DMX512 control of the LED step light by using the DMX512 controller to adjust the brightness level of the LED step light. If the LED step light does not respond or function properly, check the wiring connections, DMX512 address, and DMX512 channel settings.

Note: This is a general guide, and the specific instructions for linking a 3W LED step light with a DMX512 controller may vary depending on the manufacturer and model of the controller and LED step light. Always follow the manufacturer's instructions and consult a qualified electrician or lighting technician if you are not familiar with DMX512 control systems.