Hi Scotty,
I was just wondering, How do vehicles earth the current in non electric vehicles or even in electric vehicles, because there is no metal to earth contact in vehicles since only the tyres are touching the ground?
Where did you get the idea that Earth is required to complete an electrical circuit?
How would flashlights and airplanes work?
The frame is the ground, there is no need for the car to have an actual ground to the earth like you have in a building.
In a building you have a three wire circuit (120 volts), one hot wire, one neutral wire and one ground wire. This is alternating current. The hot wire and the neutral (typically white), complete the circuit. The ground wire is for safety. In an automobile (DC) system, the circuit is completed when current moves from the hot (positive), through the load (lights) and back to the battery through the ground (which is actually a neutral). This is a reason why motorcycle batteries generally don't last very long because when you put the metal kickstand down, you are actually grounding the circuit.
I don't buy the kickstand thing. Sounds like an old wives tale.