A guidance and navigation relay
The guidance and navigation relay, or G and N relay, was a component of a Danube-class runabout which was connected to the autopilot.
In 2370, Jake Sisko and Nog removed the guidance and navigation relay on the USS Rio Grande to disable the autopilot. (DS9: "The Jem'Hadar")
From the Star Trek Encyclopedia (4th ed., vol. 1, p. 320), "The G and N relay of the Rio Grande, removed by Jake in the "The Jem'Hadar", was actually the "head" of a small model of the Nomad space probe provided by Star Trek: Deep Space Nine scenic artist (and space hero) Doug Drexler!"