A Contract Maintenance Mechanic reports that assumption and complacency were factors involved in his maintenance errors. He installed only one lockout pin at each Thrust Reverser half on a B737-800 aircraft and did not collar a pulled circuit breaker during an MEL Reverser deferral.

Narrative

Air Carrier X's; B737-800 aircraft on flight from ZZZZ to ZZZ; returned to gate in ZZZZ. I was [Contract Maintenance] and called to address a left Thrust Reverser (T/R) fault light illuminated on the overhead panel. I went to the cockpit; verified fault and attempted reset on the Engine Accessory Unit (EAU) in the Electronics Equipment (E/E) compartment. The fault [did] reset; but re-appeared with an attempt to cycle the thrust reverser. Air Carrier's Maintenance Control was then contacted to advise of the situation and to get instructions for disposition. I was told that we would place on MEL and asked if I was familiar with the procedures; to which I responded to the affirmative. I was then instructed to accomplish the procedures and call back for the numbers for the logbook upon completion. I reviewed the [Flight Deferral] Manual provided to me by the First Officer and proceeded to comply. All went smoothly except for an illustration that showed locations for four [Reverser] Lockout Pins to be installed; but there were only locations for two pins; one on either T/R sleeve. Upon review of MEL procedures with the crew; and the First Officer physically checking the T/R; we concluded that the illustration was for another configuration; but the T/R was locked out. By my recollection; I was only familiar with T/R's with that [two lockout-pin] configuration. I pulled the circuit breaker in the cockpit; there were no collars in the [Fly Along] bag in the cockpit; so none was installed. The MEL numbers were attained from Maintenance Control and the MEL details were reviewed with the [flight] crew and the aircraft dispatched. The Company called later and advised that there were errors made in placing the system on MEL: 1) There were indeed four locations for the [Reverser] lock-out pins. 2) The Circuit Breaker was reset at some time since. I feel that there should have been follow-up to verify that there were indeed just two locations for 'lock-out' pins with Maintenance Control and not relying on past experience. I should have had Air Carrier X; fax copies of Maintenance Manual (M/M) instructions to verify applicability of illustration. I should ignore the issue of length of delay and not have allowed the aircraft to leave without a collar on circuit breaker. Carrier X should [provide] detailed procedures with Technician step by step; prior to issuance of MEL.