I have no idea which color the wires will be, but an easy way to do it would be to pull one of your tail lights off & pop out the reverse bulb to see which 2 wires are connected where it goes into the wire loom.
The plug going to the light socket will have a marking MINOR MAJOR GROUND. Trace the wire from the MINOR or MAJOR (whichever is connected, probably major) and that will be the + Positive. Trace the Ground or GND wire & that will be your - Ground.
Split the wire loom open where you have a little wire showing & use some quick taps to tap into the reverse light wires & attach your led +/- wires accordingly & you should be good to go.
If the led wires are too short, just tap the reverse light wiring with some red/black wire & run it to a convenient area where you can splice those wires into your led wiring.
Make sure to use good electrical tape to cover all the splices & connections before you put everything back together too
Test them out & if everything works, re-install the tail light & you're done.