B737-300 First Officer reports a major electrical failure after landing; including #1 Transfer Bus Light ON with OFF flags in all the flight instruments; plus other electrical issues; including no radios and Anti Skid Fail. The same fault had occurred on the previous leg with a different crew. Maintenance finds the #2 GCU loose in its' rack and re-racks to solve the problem.

Narrative

The previous crew experienced a major electrical failure after landing; which rendered them NORDO for two minutes before all electrical systems came back online on their own; including the radios. They wrote it up in the book and Contract Maintenance was called out to troubleshoot. Contract Maintenance ran extensive electrical checks with the engines running and could not duplicate the problem; so the aircraft was cleared for service. On our first leg flying this aircraft; the aircraft experienced the same electrical failure after the landing rollout. We went NORDO after exiting the runway. This time the Electric System did not restore itself. The crew could not talk to ATC. Fortunately; our gate was directly in front of us so we just taxied into the gate without clearance from ATC. The taxi distance to the gate was less than 500 FT. We had a clear path to the gate. We called Maintenance as soon as we shut down safely at the gate. ATC was not called by phone. The writeup in the maintenance book read; 'At landing/touchdown; #1 Transfer Bus Light ON with all OFF flags in all the flight instruments; plus other electrical issues; including no radios and Anti Skid Fail. Maintenance fixed the entry; 'Re-racked #2 G.C.U. (Generator Control Unit) in accordance with Maintenance Manual - ran engines and put generators on line - performed Transfer Bus Check and Standby Power Check in accordance with Maintenance Manual - all ops checked good.The #2 G.C.U. behind the First Officer's seat was not seated properly in its rack. No one detected it except the expert eyes of Maintenance Personnel in ZZZ. Had the G.C.U. come loose in the air; this would have caused major problems for the flight crew. All flight instruments including the standby gyro were rendered useless. This should be highlighted with other air crews and Maintenance Personnel throughout the system.