It comes with the kit! Buy RAA623 from any dealer. That's all you need.
I don't understand why ppl have said "I don't do electricals" etc when it's so easy. Remove RHS Rear wheel, remove black plastic with 2 screws from memory and Plug it in the socket, simple.
If you have paid someone to install for you, sorry but you have been ripped off! Most dealers ( outside of LR) do a terrible job at it anyway poorly splicing straight into the tail light or even getting it wrong completely. I had park/number plate light come on instead of brakes from the Jeep factory

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