parasitic power loss?

From a technician stand point there are a few thing to consider when doing a closed circuit current measurment (parasitic draw) test.

First, the meter must be hooked up in series, but you must be careful when beginning the measurment not to blow the fuse.  As auex stated all the loads in the vehicle must be off.  However,  if you do see a draw of over 50mA after 30 min to 1 hr. you dont want to have to open the doors to get to fuses and different components.  So in that case leave all the door and trunk open, but latch all the latches to simulate the doors being closed.  If you do have a draw start pulling fuses to eliminate different circuits.  When the draw goes away you've found the circuit that is causing problems. 

Also, be careful on some later GM vehcile as some of them have an after-blow feature to keep the evap core dry.  This causes the blower to kick on at different times.  This will blow the mA fuse in your meter.  Also keep in mind that if for some reason your meter looses connection this will open the circuit and upon reconnection some modules will be woken up causing possible false draw mearurment.