How many watts are the lights? Are you sure the wire from your reverse lights is heavy enough? Divide watts by 12v and that is the amp draw, use the amp draw to size your wire. You also need to have a good ground. Theres a spot above the spare tire towards the front of the truck you can ground to. At least there is on my 09, yours might be different. I never really liked tapping into stuff for this reason. You might want to consider putting a switch in and running wire.
Black 2009 Platinum Screw 4x4-5.4, 3:55 gears
MODS-Stainless works exhaust, Boss coilovers kit, firestone airbags, Raptor wheels, BFG KO 315/70R17, Edelbrock SC