The simplest is to put a switch under the dash. When backup lights were first put on, that's how they were switched. Connect the wire to any hot wire and run it to the switch then the light. Make sure the light is grounded. Mine is connected to the switched side of the ignition switch so that it's dead any time the key is off to prevent an accidental drained battery.

Save a life, adopt a senior shelter pet.
The three main causes of blindness: Cataracts, Politics, Religion.
Name your dog Naked so you can walk Naked in the park.