The **side position lights** are essential to **indicate the presence of the vehicle**. These lights are designed to make the vehicle visible and to identify its width, especially in low-light conditions or when parked in poorly lit areas.

- **Location of the position lights**: They are located at the front, rear, and sides of the vehicle, which helps make the vehicle visible from different angles.

- **Use of the position lights**: They are used when driving at night, passing through tunnels, or on dark days with little natural light. They are also turned on when the vehicle is stopped on a poorly lit road due to a breakdown.

Therefore, the main function of the side position lights is to ensure that the vehicle is visible to other drivers and pedestrians, thus indicating its **presence** on the road.