Voltage drop at ballast resistor

When you say dual resistor do you mean 4 pole? My car has the 2 pole resistor.
Yes. Its two resistors. The 5.0 ohm resistor is to power the ECU.

To amplify on 'downstream'.
When the engine is off, or the alternator not producing power, the battery positive is the highest voltage. When a circuit is completed, power flows downstream from the battery.
When the alternator is producing power, its output terminal is the highest voltage, from there all power flows downstream to ground.