Where is the 4WD actuator located on a 2003 Chevy Trailblazer?

The 4WD actuator on a 2003 Chevy Trailblazer is located on the passenger side of the transfer case. It's usually fairly close to the transfer case itself and might be somewhat hidden depending on the specific model and trim level. You'll likely need to get underneath the vehicle to locate it. It's a relatively small, cylindrical component with electrical connectors.