A controlling device for use with an exterior landscape lighting assembly. The lighting assembly includes a transformer having an input line connected to an electrical power source. The transformer converts a primary electrical load to a secondary electrical load which is in turn outputted though an output line connecting to a plurality of individual lighting units. The controlling device is capable of being mounted at an appropriate location indoors or outdoors. An enclosure unit includes a power supply circuit, a switch, a relay and control circuitry. The power supply circuit converts the secondary transformer output to a filtered direct current suitable for powering the control circuitry. The control circuitry interfaces with remote momentary switches and alternately activates and deactivates the lighting units. The control circuitry further includes an optional receiver for wireless operation. The controlling device can be incorporated into the transformer assembly.