Last weekend I got my rear fogs working without buying anything from Mopar.
I have a 2019 Rebel, which already had 1 rear fog wire running to the rear bumper but not in the bumper harness. It's a White/Orange wire, with nothing on the other side of the connector.
You need alfaobd to activate rear fogs.
Also need a relay since most LED pods consume more current than the Mopar rear fogs.
I'd recommend adding a fuse, and some kind of indicator. My factory gauges don't have a rear fog indicator, but has a useless vta light, so I used that. If you already have the rear fog indicator or don't want one, you won't need to do anything under your dash.
Stock fog light switch will work. The only difference between stock and the "rear fog" version is the symbol painted on the button.
Supplies needed
-Alfaobd & OBD2Link MX+
-Standard Bosch relay preferably diode type
-Fuse holder with fuse
-soldering iron and heat shrink with hot melt (preferred), or just use crimp connectors with hot melt. They'll last until after the vehicle dies
-wire. Preferably red and black 14awg is probably fine unless your lights are stupid bright
-stripper/crimper/cutter, basic tools
-split wire loom, loom tape, zip ties
-EP35 electronic flasher if you want the indicator light to blink
Will add links to the specific parts/tools I used later