Car not starting

[SeattleBimmer]

Update: Tested voltage drop under load.

1) Confirmed battery was charged. Battery read 13V at terminals under the hood without load. Started the car to confirm problem still existed. No start.

2) Pulled the spare tire to get to the battery. Inspected the BST. There weren't any signs that the BST was triggered. Wiggled the cable to see if it was ejected by the BST. It was solid, no wiggle at all.

3) Connected the leads of my DVOM to the positive battery terminal directly on the battery in the trunk to the positive terminal under the hood. Voltage read 0v (without load). Held the key in the ignition position and the voltage jumps to 11.10v for about 2 seconds then drops to 4.5v and continues to stay at 4.5v even after turning the key off. Can someone explain that???

4) Left the DVOM lead connected at the battery positive terminal and moved the lead under the hood to the the ignition switch. Tested both sides of the ignition switch (power supply pin, and starter pin). Under load, the voltage reading showed between .1-.2 volts which I understood is within specifications.

So If i'm understanding this correctly, the voltage didn't drop beyond the specified range from the battery to the ignition so we can rule out everything in between. From the bentley diagram, the BST appears to be on a parallel circuit so that has not been ruled out beyond visual inspection. Can someone confirm that? Is the engine bay terminal connected to the battery by one long continuous cable? If so then we can probably conclude the problem is somewhere on that cable or at the end connections of that cable.