Just discovered previous owner did a modification to the interior overhead light assembly

While flipping my my rear view mirror upside down, I noticed a cable coming out of the interior overhead cover where the lights and sunglass holder is:



So I did some more investigation by taking out the assembly (which the previous owner clearly had already done since the screws holding that thing up there were gone), and I found this:



I have a pretty good guess what this is for. The previous owner had a backup camera installed, but I am missing the wireless monitor that works with the camera (I started a thread on it here). I assume he used this to power that monitor (which I still don't have).

Could I install a radar detector or something else here? I am not familiar with wiring stuff, so I am just curious what I have on my hands. I know the previous owner was very much into this kind of stuff. I would ask him, but unfortunately he is dead .

Thanks for your help.