An actuator circuit was an engineering component on Vulcan D'Kyr-type starships and Xindi-Insectoid shuttlecraft. Aboard the latter vessel, the port actuator was a switch in the craft's cockpit, on the port bulkhead.
In 2153, Lieutenant Malcolm Reed realigned the actuator circuits on the Seleya. When T'Pol checked them, she got zapped and blamed him, saying they weren't sequenced properly and that he had been overloading the locking mechanism. After Jonathan Archer suggested they try another fix, she dismissed his suggestion, claiming the circuits were beyond repair. Paranoid, she further suggested that it was a deliberate sabotage. (ENT: "Impulse")
While Commander Charles Tucker III and Ensign Travis Mayweather were endeavoring to learn how to pilot a Xindi-Insectoid shuttlecraft in 2154, Tucker tested Mayweather by asking him to "try the port actuator", a request Mayweather complied with. (ENT: "Azati Prime")