Commercial Fixed Wing
Maintenance Powerplant; Maintenance Airframe
Communication Breakdown; Confusion; Distraction; Situational Awareness; Time Pressure
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy
General Maintenance Action
Aircraft; Human Factors
Aircraft X came to the gate; originally a gate call for another employee who was timing out at XA:00pm.  I was asked by my lead to relieve him of his duties.  The pilots ran the system hydraulics # 2 motor and reported pressure was good but the low-pressure light continued to stay on.  Deferred low-pressure light for indication problems per MEL XX-X-XX Special Procedures (SP1 and SP3).  SP3 said I could either disconnect the cannon plug or leave it attached.  Crew wanted it disconnected; to do away with light in cockpit.  Proceeded to disconnect the plug.  After takeoff; flight crew called back on the radio and stated that the light was still on.  At that point I double checked myself with the MEL and maintenance manual and realized I disconnected the wrong cannon plug.  I was supposed to disconnect the one in the wheel well when I actually disconnected at the engine hydraulic pump.  I reported the mistake to maintenance control and they stated that it would be fixed by contract maintenance upon arrival in ZZZ.  [Recommend to] be more aware and not jump from one plane that was Out of Service (OTS) to take over something when your knee deep into another plane. Tell the lead to go to the next person. Evening shift.
A Line Aircraft Maintenance Technician (AMT) was asked to take over the duties of another AMT who was leaving in the middle of an ongoing MEL Special Procedures task for deferral of a Low-Pressure Light hydraulics indication problem. The Relieving Technician finished the maintenance. A flight crew later reported that the light was still on. The Relieving Technician had disconnected a Canon Plug at the # 2 engine hydraulic pump instead of the # 2 electric pump in the wheel well.