I bought a used 2018 superduty with out the factory bed lights, since ford doesn't sell them after market for the superduty, does anybody know the three correct wiring harnesses to hook up the lights? I have a xlt with gas engine, and backup camera.

 

Welcome to the site.
The bed lights are/were a SD option, so you should be able to order the parts from your dealer as replacements. If you install OE lights and utilize the harness connectors the feature has to be turned On within the BCM. Pretty sure the XLT would have feature/control provisions. If the 2 pin harness connectors are there ( should one each,, L/R sides under the bed about where the tailgate pivots would be only along the bed harness extension, you should be good to go..
You can do the program task with FORScan.. Same goes for the 150’s, when adding illumination, the programming needs to be done to activate the connectors
There’s aftermarket stand alone hard wire units as well.