A Line Mechanic reports he did not re-connect a cannon plug to an override fuel pump when he tried to replace a nutplate on a B767-300. Aircraft returned to blocks with fuel pump pressure problem.

Narrative

Maintenance Control assigned item a Priority-1; replace nut plate on override pump panel. In order to gain access to the nutplate; I had to remove the cannon plug for the override pump to see the area for the nutplate. The cannon plug continued to get in the way of my research of the area. So I put the cannon plug up in the pump area to get it out of my way.I left the ramp to inform the Supervisor that it would need a tank entry to work the assigned job. Upon returning to the aircraft I found stairs up to the aircraft and called for a Supervisor to come out to see the stand at the aircraft so that I could not get in trouble for the stand being there without anyone at the aircraft.Ramp came out to tow the B767-300 to replace broken aircraft on a gate. With panels open; Ramp refused to tow aircraft. They left the aircraft and left stand up to aircraft; which is a security violation. My Lead informed me that the aircraft was re-routed and we needed to get off of it right away. I put the panel up and had the other Mechanic hold it in place as I got the screws and started to put the screws in place. Then left the aircraft for the Ramp to tow. I overlooked the cannon plug not being re-installed. The plane returned to blocks with a pump fuel pressure problem.