Demisting and Ancillary Controls on Your Driving Test in 2026: The Switches Examiners Expect You to Find

There is a marking box on the examiner’s DL25 form labelled “ancillary controls”, and most learners never think about it until the windows fog up on a cold morning and they cannot remember which button clears the rear screen. It is one of the easiest faults to avoid and one of the most avoidable ways to make the rest of your test harder than it needs to be.

Ancillary controls simply means every control in the car that is not the steering, pedals or gears: wipers, washers, headlights, the demister, heated screens, the heater and ventilation, the horn, and hazard warning lights. The examiner is not testing whether you know the manual. They are checking that you can operate them safely, at the right time, without taking your eyes off the road for longer than a glance.

Why This Matters More Than It Sounds

A misted windscreen is a genuine safety issue. If you cannot see, you cannot make safe observations, and everything downstream — junction checks, mirror work, hazard perception — degrades. Examiners rarely mark the mist itself. They mark what happens next: the missed pedestrian, the hesitant junction, the late observation.

Equally, taking your eyes off the road to hunt for a switch is what turns a minor irritation into a fault. If you look down for three seconds at 30mph, you have travelled roughly 40 metres blind.

How to Clear a Misted Windscreen Properly

The fastest method is not the one most learners use. Misting happens when warm, damp air meets cold glass, so the solution is drier air, not just hotter air.

1. Turn the fan up high and direct the airflow at the windscreen.
2. Switch the air conditioning on if the car has it. Air con dehumidifies, even when set to warm, and clears mist far faster.
3. Turn off air recirculation. Recirculating damp cabin air makes misting worse.
4. Switch the rear demister on at the same time.
5. Warm the air gradually once the mist starts lifting.

Do all of that before you move off if you can. If it happens mid-test, deal with it — the examiner would far rather you adjusted the demister than drove on peering through a patch of clear glass. If visibility is genuinely poor, it is entirely acceptable to say so and pull over safely when there is a suitable place.

When to Use Each Control

Wipers. Use them as soon as the screen needs it, and turn them off when the rain stops — smearing a dry screen is a control fault. Learn where the intermittent setting is for light drizzle.

Headlights. Dipped beam whenever visibility is reduced, not just after dark. Low winter sun, heavy rain and gloomy afternoons all qualify. Many modern cars have automatic lights; know whether yours does and check they are actually on.

Rear fog lights. Only when visibility drops below roughly 100 metres, and switch them off promptly afterwards. Leaving them on dazzles the driver behind and is an offence.

Hazard lights. Only when stationary and causing an obstruction, or to warn of a hazard ahead on a fast road. Never as an excuse for parking badly.

Horn. To warn others of your presence. Not in anger, and not in a built-up area between 11.30pm and 7am while moving.

The Cockpit Drill Connection

Most ancillary control problems are prevented before you turn the key. When you set up the car, take an extra ten seconds to locate the demister, the wiper stalk and the light switch, and to set the heater somewhere sensible for the weather. If you are taking the test in an unfamiliar car, this is essential rather than optional.

It also pays to think ahead about the weather. On a frosty morning, clear all the glass before you set off — not a letterbox in the frost. On a wet day, check the wipers work and that the washer bottle is full. A car that cannot demist or wash its screen may be judged unsuitable for test.

How This Links to Show Me, Tell Me

The “show me” question is asked while you are driving, and several of them are ancillary controls in disguise: showing how you would demist the front screen, wash and clean the windscreen, switch on dipped headlights, or operate the rear demister. Practise doing these while moving, with a quick glance rather than a long stare, and without wandering out of your lane. That is exactly what is being assessed.

Practical Habits That Stop This Becoming a Fault

1. Learn the switches by touch in the car you will actually use for the test.
2. Set the climate controls before you move off, not at the first roundabout.
3. Use air con plus fresh air for fast demisting, whatever the season.
4. Glance, do not stare. If a control needs a long look, wait until you are stationary and safe.
5. Turn things off when they are no longer needed — fog lights and wipers especially.
6. Do not fiddle. Constant adjustment reads as distraction.
7. If visibility is unsafe, act. Pulling over safely to clear the screen is good driving, not a failure.

Frequently Asked Questions