Not uncommon for owners to fit extra lights and reflectors on series trucks, I actually was pulled over by the local police he complained about the lack of rear lights, You will have to trace some wires to see when they come on, how they work,
Ah, extra brake lights. Hadn't considered that when I posted a response earlier, but should have since I did it to mine too.
Mine is an LED rear fog light out of an LED kit for a Defender. The Defender didn't have a rear fog light so the tech at the LR dealership I was visiting gave it to me. I installed it on the rear door and wired it to the regular brake lights. Nice and bright!
BTW, didn't mind drilling holes in my rear door since I'd already made it "non-original" 25 years ago by cutting it in half so I could use the bottom half when driving with the top off.