The CLP/SSM are powered by fuses 25 and 26 and this power does not "come thru the key", those are battery feeds and are hot at all times. If you don't have power on BOTH, you must fix that FIRST.

The BCM signals the CLP/SSM in the following manner:
1) The driver's door lock cylinder has two wires that run to the SKREEM to tell it when the key in the door turns the cylinder. The SKREEM has two more wire from it to the BCM so the BCM knows to tell the CLP/SSM to lock/unlock the doors and that the command came from the door cylinder.
2) When you use the lock or unlock buttons on the key FOB, there is a single wire from the SKREEM to the BCM, this is a bidirectional data line that the SKREEM uses to tell the BCM that the key FOB has sent an unlock or lock command. The BCM then tells the CLP/SSM to lock or unlock and that this is a command from the key FOB.

THese are SIGNALS, not power, being sent to the CLP/SSM. These signals travel over the separate CAN bus that connects the BCM, CLP/SSM and Power Top Control Module. (This is not the CAN BUS that the other modules are on that control the engine, automatic transmission, brake controller, etc..)