The operation of vehicles is prohibited if:

Explanation

When the steering system contains parts or assemblies not provided for in the vehicle's design.

The list of defects prohibiting the operation of a vehicle treats the steering system more strictly than any other part. It is enough for one part or assembly not provided for by the manufacturer to be used in the steering — a non-standard bolt, an arm end from another car, home-made welding on a steering rod — for driving that vehicle to be prohibited. The issue here is not "does it work or not"; the mere presence of the foreign part is the offence.

The safety reason goes back to the architecture of the vehicle: the steering is the only vital system with no backup. The service brake has a dual circuit and the parking brake beside it; but if a steering joint separates in a bend, no alternative mechanism exists and the vehicle becomes uncontrollable at that instant. A non-original part also fails at precisely the worst moment: under the greatest force, that is, mid-bend or during a sudden manoeuvre to avoid an obstacle.

This question's trap is the lamp colour option. Memorise the colour rule separately: white light is permitted at the front, and the prohibition concerns red light at the front and white light at the rear. So a white lamp at the front is no offence and invalidates the "in both cases" option.

• White at the front is exactly what the standard expects; the colour prohibition is on fitting red light at the front or white light at the rear, not white at the front. • Since the second item is not an offence at all, "in both cases" cannot be correct; only the steering fault prohibits operation.

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