I had a brake light pulser that I removed from my leased Leaf. Because I extended that lease to 3.5 years I likely paid $300 to $400 for it.
To remove the panel with the brake light start by removing the 4 bolts to on each side from inside the trunk. Pull hard on the panel and it will pop up from those white pins two on each side. The center black pin I pushed from inside the trunk. To remove the inside cover use a wide flat screwdriver in the little slot on the right to release the first clip. Pull hard at the window side and the panel will pop out. It has eight of those locking white pins.
There are two screw holding the third brake light assembly in place. The black wire is the minus. The black/white is the wire the pulser needs to be put in series.
Here are some pictures: https://drive.google.com/folderview?id= ... 5pvz7aek4F