It seems that all of the sudden today I have a voltage problem in my 01 GTP. I Checked the power distribution box, alternator, and battery terminals. I want to check the connections at the starter itself but I can even see them from under the car. Anywhere else I can check besides there? I'm goign to try and wiggle my hand up in there to tighten them but where else could I check? I dont even know where all the grounds are in this car.

Oh yeah, what's happening...
When I turn the key to on, the fuel pump barely runs and all of the dash lights are very dim, and of course if I turn the key to start all I get is a single click of the starter relay and everything goes black till I let go of the key. After I've let go the door locks go UNLOCK UNLOCK by themselves. The voltage at the battery is 12.3 volts. The voltage at the Fuse box is also fine with the volt meter. I dont have the slightest clue as to what happened all of the sudden.