Do you mean the sensor is not installed in the cold light? If installed you just put the stabilizer plug into the sensor receptacle on the light. Plug the cold light AC into the stabilizer and the stabilizer AC into your timer. The cold light heater goes directly to an AC outlet. If not installed the sensor should be attached to a receptacle that the stabilizer cord plugs into. You need to drill or punch a hole for the receptacle into the top of the cold light housing. Mount the receptacle on the housing and position the sensor within the head so that it is looking at the light. Plug things together and see if the stabilizer works properly. Mine is set at position L but that probably varies. Once you position the sensor properly hold it in place with a small cable tie to, if I remember, the lamp itself. I bought a sensor for mine years ago and installed it. Could still have the instructions. I can look if you need them.