What is the difference between FMVSS: PC and FMVSS: P2?

P2 is the minimum standard for clearance, side marker, and identification lights. All Truck-Lite lights meet this standard, even if they are marked PC, P3, etc.

PC lights are to be used as a combination light, meaning the light should be mounted on a 45° bevel at the corner of the vehicle, allowing clearance and marker functions to be combined into one light.

A PC light can always be used anywhere a P2 light would have been used, but the reverse is not true.