Laser LA03-5000 wiring to RAMPS 1.4
Please look into this question, this is a very similar question and also involves PWM and a RAMPS 1.4 shield. 

In your case you connect the top red wire on the right bottom connector to the D4 pin and adjust the firmware accordingly as described in this answer.

The bottom 2 wires of the lower right connector should be connected to ground and 12&nbsp;V (resp. black and red).