Courtesy light wiring?
So you need to use both the power and ground wires of the courtesy light circuit from the BCM to make additional lights work the same way. The power wire is the dark blue with white in the 6-pin black BCM connector. The return (ground) wire is the white wire in the 32-pin blue BCM connector.
Don't cut either wire - just tap into them for your power and ground. Be careful that you get the correct wires... they are the only ones of those colors in those connectors but there are similar wires (e.g. there is a white with black wire close to the white wire in the 32-pin blue connector and there is a plain blue wire close to the blue with white wire in the 6-pin black connector).
The BCM is relatively easy to reach, doesn't have duplicated wire colors, and gives you all the features of the existing courtesy lights. I recommend making your connections there.






