There is a couple ways you can wire them up.
If you wanted to have them duplicate the functionality of the main tail lights, i.e. break, blink, shine

you would tap into the tail light relay module in the trunk.
I wanted them to be strictly to be on when the lights come on, without anything else, so I connected mine to the side marker light.
I honestly didn't feel there was a need for a relay, I had no problem with the way I hooked them up.
I started with single strip first, then a year later I swapped it out for a dual strip.