BCM Pinout needed?

I wouldn't connect anything to the BCM or the lighting module directly, the outputs are not designed to carry much of a load and adding more lights can easily burn the control circuits out, especially on modern vehicles where they have gone so far as rate the wire sizes for the minimum loads. Instead I would go to the lights that you want the new lights to work with and install a relay that can turn on when that light comes on, so if they are LED lights for the running boards, tap into the trailer park lamp fuse (F41) that sends power when the marker lights are on. Have that wire turn the relay on and use the relay to switch on the power to those LEDs. Just add a fused power feed from the battery feed post on the side of the fuse box under the hood. If you are looking for one to turn on a stop lamp that is independent of the turn signals you can add a fuse tap to the CHMSL fuse (F53) in the same under hood fuse box.
As for what the wires at the BCM are, GM has not sent the wiring diagrams for the 2025s out to the aftermarket repair services yet.