That "plug" isn't under the seat visibly. It's actually a sensor in teh locking part of the seat belt, wire runs down the seat belt part and under the center console.

2006 Pontiac G6 3900SFI GTP Coupe CAI, Stainless Cat Back, Vector Tune, Strut Brace, Eibach Pro Kit, Custom Made Projector Headlights, 4300K, 20% Tint Former Owner- 2000 "Stryped" CSVT CEG Dragon Run- Oct 13-15