The operation of vehicles is prohibited if:

Explanation

Both the loss of sealing in the hydraulic brake actuator and the fitting of white indicator lamps at the rear.

Both items are on the list of prohibiting defects; one from the brakes category and one from the lamp colours category.

A hydraulic brake works on a simple principle: fluid is incompressible, so the pressure of your foot reaches all four wheels undiminished. The moment the circuit's sealing fails and air or a leak enters the system, that chain breaks; the pedal softens, its travel lengthens, and at worst it goes to the floor without the car slowing. The main danger of this defect is that it is hidden: in gentle urban braking you may feel only slight softness, but in the first emergency stop all braking capacity is lost. That is why no degree of leakage can be overlooked.

A white indicator lamp at the rear is also an offence, because indicator colour must be yellow/amber on both sides of the vehicle. White light at the rear has another defined meaning: reversing. On seeing white light the driver behind thinks the car in front is coming towards him, when it merely intends to turn; or, conversely, he fails to grasp the intention to turn and pulls into its path.

The rule: every colour on a vehicle's lamps carries a unique message; swapping colours means sending a false message.

• Correct but incomplete; the loss of sealing in the hydraulic brake circuit really does prohibit operation, but this option ignores the white rear indicator item. • A white indicator at the rear is independently an offence too, but choosing it alone means you have dropped the brake defect from the answer.

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