When installing our bed lighting kit for the Ram 1500.
You are required to Pin into BCM connector C1 on Pin 5.
The diagram below will give you a visual of the BCM, the C1 connector, and Pin 5 on C1.
Make sure this connection is secure and the grounding ring is attached to a grounding point in the vehicle.
If the bed lights don't light up but the third brake light does then the pinning job needs to be checked over, as well as ground.
You can test to see if the bed lights work by connecting them to a 12v source and ground, if they light up then they are good lights.