B757-200
Maintenance Airframe; Maintenance Powerplant
Distraction; Communication Breakdown; Fatigue; Workload; Situational Awareness
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy
General Maintenance Action
Aircraft; Chart Or Publication; Equipment / Tooling; Human Factors; Procedure; Weather
After the gear down handle replacement there's an Operational Test; AMM Chapter 31-61-00 of the landing gear sensors.  Had to 'activate' and 'deactivate' landing gear and [landing] gear door sensors; while watching cockpit for certain messages.  After aircraft passed the [Ops] Test; started removing activators and deactivators from B757-200 aircraft. Started in the nose gear then moved to the Main Landing Gear (MLG). Went to the right side MLG.  Went up on the ladder and removed all activators and deactivators.Moved the ladder to the left and did the same. I had a second person walk around the aircraft to make sure all activators and deactivators were removed. The left MLG uplock sensor was supposedly left on. I thought I had removed all test equipment and pins. The uplock activator is in a hard place to see even with the  [safety] streamer on. There was high winds all day and the going up and down the stairs all day might have added fatigue to the situation.
A Line Mechanic reports he may have left an 'activator/deactivator' installed at the left Main Landing Gear (MLG) up-and-locked sensor on the uplock assembly of a B757-200 aircraft; after an Operational Test for a landing gear handle replacement.