Final answer:
The primary connection D-ring on a harness should be located on the back, which is vital for safety during work at heights.
Step-by-step explanation:
The primary connection D-ring on a harness should be located on the back. This D-ring is a critical component for attaching a lifeline or lanyard for fall protection, ensuring the safety of a person who needs to work at height. The back location of the D-ring provides the best support for the body in case of a fall, distributing the impact forces over a larger area of the body and reducing the risk of injury. It is essential that the harness be properly worn with the D-ring in the correct position for effective safety.