A system for mounting a light emitting diode (LED) wave guide down light retrofit fixture. The system can include a mounting plate having a number of apertures symmetrically positioned around a center of the mounting plate. The system can also include at least one fastening device mechanically coupled to an upper surface of the mounting plate using at least a first aperture of the apertures, where the at least one fastening device mechanically couples to a base of an existing fixture. The system can further include a coupling device mechanically coupled to a lower surface of the mounting plate. The system can also include a trim assembly having a frame and a LED light source mechanically coupled to the frame. The frame can have a coupling feature disposed on a top surface of the frame, where the coupling feature mechanically couples to the coupling device.