main electrical power short?

I have had this issue several times during my ownership of the car. It happens very occasionally and at random times (doesn't matter if the car has been running recently or sitting for a day or if it is hot of cold out). Usually it starts on the second attempt but twice now it has taken over a day and many attempts to get the vehicle to start. What happens is that the power to the entire car shorts out when I draw power from switched or constant power sources. Every time this has occurred the engine has been off, I have never had the engine stall while running. When the power cuts out, it cuts out to the entire car, voltage remains the same at the battery (12+ volts) but when tested at either the jump starting post under the hood or at the fuse box I get readings of 3-4 volts which quickly drains (residual power from when they were "hot" I'm assuming). Power cuts back on usually after about 30 seconds but shorts out again when I draw from it. Also voltage is good at the battery connectors (the clamps where the cables hook up to the terminals) so it seems the connection is good there. ECU and gauge cluster can be ruled out, I tried disconnecting them both but still had shorts occur with the key in position 1 and 2. It's as if there is a breaker tripping and then cutting back on. Could it possibly be the voltage regulators?