Why you ask? For me, track days. I can have my phone charging, while also using the cigarette lighter / aux power port to use for a portable air compressor. See for yourself, it’s handy!
FWIW, this is what I purchased. It’s kind of crappy, and has actually failed me, so I suggest finding a better alternative. Either way, the installation should be very similar to other products.
Positive Connection, un-fused post.
Negative Connection, existing ground point. Also showing inline fuse in the positive lead.
This position for the device is out of the way of the trunk lid arm and battery junk.
I realized that I put it in the wrong orientation, the flaps should swing to the left instead. Oh well! Don’t forget to turn it off!
I’m sure you all can fill in the blanks, you’re smart cookies.