Are you not even getting the 2-second power shot when you first turn on the ignition (before you crank the starter)? If you turn on the ignition then walk back to the trunk to measure the voltage, you will have missed it. You need to place the volt meter in view of the drivers seat so that you can see if there's momentary voltage when you first turn the key on. And then watch the meter as you're cranking the starter. After making these two observations you can start to narrow down the possibilities.