Motor vehicles must have turn indicator lamps if the

Answer: B — Body or load extends 24 inches or more to the left of the corner

The requirement for motor vehicles to have turn indicator lamps is specifically tied to safety and visibility when the vehicle's body or load extends significantly beyond its standard dimensions. If the body or load extends 24 inches or more to the left of the corner, it creates a greater risk of obscuring the vehicle's intended path during turns. Turn indicator lamps are essential in such cases as they signal to other drivers the vehicle's intention to turn, which is vital for ensuring the safety of all road users. Having turn indicators in this scenario allows for better communication of movement intentions, reducing the potential for accidents caused by a lack of visibility or misjudgment of the vehicle's path. Other dimensions like extending only 12 inches to the rear, exceeding a height of 13 feet, or having a width that exceeds 8 feet do not impose the same level of risk related to the visibility and communication of vehicle maneuvers. Therefore, regulations highlight the 24-inch extension rule as a crucial threshold for requiring turn indicator lamps.