A Mechanic reports about verifying a left engine air/oil heat exchanger valve was open; as a requirement for an MEL 75-21 deferral on a B767-300; but mistakenly disconnected the electrical connector for the PW-4000 IDG air/ oil heat exchanger valve instead.

Narrative

A B767-300 inbound crew wrote up the following irregularity: L Eng EEC C1; L Eng Air/Oil Valve; dispatch was approved for MEL 75-21-02A. The Left PIMU was interrogated and verified the fault as follows: EEC \Ch-A and Ch-B AOC TR-CK Fail and AOC FD-BK Fail - Flight Leg 1.The dispatch manual states to verify that the valve is open and if so; remove and stow the electrical connector from the Air/Oil Heat Exchanger. AMT verified that valve was indeed open; but removed the electrical connector from the IDG Air/Oil Heat Exchanger by mistake. The respective valves are located opposite of each other on the engine; (IDG valve is on the right side and engine A/O valve is on the left). Both coolers and valves are of the same type and style.Previous experience not withstanding and an incorrect judgment (human error) by the AMT; along with a miscommunication from Maintenance Control over the phone; resulted in the error. Problem was discovered by the flight crew; after taxi out and departure. Maintenance Control was notified by Maintenance; with additional corrective action to be addressed at the flights destination. Aircraft did not return to gate; or off land at another airport enroute. Flight proceeded normally and on schedule.