Here is a basic model capturing how electricity fits into a car's functioning. Hope to make it more sophisticated as I learn. This web page will be a good resource: How Car Electrical Systems Work 
digraph { node [shape=box style=filled] Battery node [fillcolor=white] Battery -> Fuses node [fillcolor=yellow] Alternator -> Battery [label=charges] node [fillcolor=lightblue] Fuses -> Starter Fuses -> Headlights Fuses -> "Dash Instruments" node [fillcolor=lightgreen] Fuses -> "Interior Lights" Fuses -> Radio Fuses -> Sunroof node [fillcolor=pink] Starter -> Engine [label=starts] Engine -> Alternator [label=drives] }
This is not a proper electrical schematic, it's meant to be a high-level description of how various systems interact. More detailed, more electrically accurate diagrams will be helpful too. (See Graphs Made of Parts)
A Parasitic Draw could occur in any of the specific components/systems the battery powers (blue=core, green=non-vital), or in the wiring that connects them to the battery. (See Golf with Rain Problem)
To do
1. Represent fuses 2. Create more detailed / accurate graph(s) of parts 3. Figure out how to manipulate graphs (e.g., separate lines for blue & green for readability?)
Diagram for Golf TDI starting system from TDI Club