I found that could pull down the headliner directly above the rear sliding window and get enough room to get my hand up in there. Inside are two 10mm nuts on bolts with a long alignment "nose" on them. It takes a small ratchet drive and a LONG 10mm socket. I found one that was around three inches long. Once those nuts are off, the light assembly will pull loose from the outside. There is a gasket in there that you need to pull carefully or it will come apart. I routed the micro-coax under the rubber grommet, the into the headliner, across to the side of the truck and down behind the door gasket. My receiver is under the drivers seat, so it was easy from there.
Once you get the nuts back on, over the alignment nose, tighten them evenly until they are snug. Make sure the coax is clear and just press the headliner back into place, it's pretty resilient. I created a couple of wrinkles in the headliner material, but they have faded and are now gone