Rear Fog Lights in New Zealand: When to Use Them, the Law, Bulbs and the WoF
In this guide
- What Are Rear Fog Lights
- Why Are Vehicles Fitted With Rear Fog Lights
- When to Use Rear Fog Lights
- Why Rear Fog Lights Must Not Be Left On
- The Rear Fog Light Symbol
- New Zealand Rules: Which Vehicles Need Rear Fog Lights
- How Rear Fog Lights Are Fitted
- Rear Fog Light Bulbs
- Rear Fog Lights and the WoF or CoF
- How to Replace a Rear Fog Light Bulb
- Rear Fog Lights on Tractors and Trailers
- Frequently asked questions
Rear fog lights are bright red lamps at the back of a vehicle that, in New Zealand, you should switch on only in fog, mist or other conditions where visibility is seriously reduced, and switch off at all other times. They exist so drivers behind can see you when ordinary tail lights disappear.
That is the short answer, and it reflects the New Zealand rules and the Road Code: fog lamps are for fog and similar poor-visibility conditions, not for general night driving. The rest of this guide explains why vehicles are fitted with rear fog lights, how they differ from tail and brake lights, the dashboard symbol, which vehicles need them under New Zealand rules, the bulbs they use, what the WoF and CoF check, and what applies to tractors and trailers.
What Are Rear Fog Lights
A rear fog light is a red, rear-facing lamp designed to make a vehicle more readily visible from behind in fog. It is far brighter than a tail light and is switched on and off by the driver with its own switch, separately from the other rear lamps.
Every car has several red lamps at the back, and they are easy to confuse:
- Rear position lamp (tail light): a dim, steady red light that comes on with the sidelights and headlights. Usually a 5W filament or a low-power LED.
- Stop lamp (brake light): a brighter red light that comes on only when the brake pedal is pressed. Usually 21W.
- Rear fog lamp: a bright red light that stays on until you switch it off. Usually 21W, in a lamp designed to throw that light out to the rear with high intensity.
Most cars and vans that have one carry the rear fog lamp in one of the rear lamp clusters or in the rear bumper. Older vehicles, trailers and farm machinery often carry a separate, standalone rear fog lamp bolted under the bumper or on a lighting board.
Why Are Vehicles Fitted With Rear Fog Lights
Vehicles are fitted with rear fog lights so that following drivers can see them in fog early enough to slow down. Fog scatters light, and a 5W tail light that is easy to see on a clear night fades to nothing within a short distance in thick fog. A rear fog lamp is many times brighter, so it punches through far enough to give the driver behind a warning.
Rear-end collisions in fog follow a familiar pattern: a driver closes on a slower vehicle faster than they realise because they cannot see it until the last moment. A bright rear fog lamp gives that driver an earlier cue. At 80 km/h a car covers roughly 22 metres every second, so every extra metre of warning matters.
That is also why they are common on European vehicles, where they have long been required on new cars and heavy vehicles under the UN ECE installation rules. Many of the cars, vans, trucks and tractors imported into New Zealand from Europe and the UK carry one as a result (the details are in the legal section below).
When to Use Rear Fog Lights
Use rear fog lights only in fog, mist or other conditions where visibility is seriously reduced, and switch them off as soon as conditions improve. That is the New Zealand position, from the lighting rule and the Road Code.
What the Rules Say
- Fog lights: use them only in fog or similar conditions where visibility is restricted. Turn them off at all other times.
- Driving in fog: use dipped headlights together with your fog lamps, reduce your speed and keep a safe distance from the vehicle in front.
- Dazzle: the Land Transport Rule: Vehicle Lighting 2004 says lamps must not dazzle or confuse other road users, and a rear fog lamp in clear conditions does exactly that.
UK guidance uses a “cannot see more than 100 metres” test. New Zealand does not set a fixed distance, so judge it by whether visibility is genuinely restricted.
Fog, Snow, Rain and Spray
Fog and mist are the conditions rear fog lamps are made for, and heavy falling snow can be just as bad on high country roads. Ordinary rain, drizzle and road spray are a different matter, and in those conditions rear fog lights usually cause more problems than they solve. Slow down and use dipped headlights instead.
When to Switch Them Off
Switch rear fog lights off the moment the fog lifts. If a car is following closely behind you in fog, its driver can already see your normal tail lights, so the fog lamp may only be dazzling them. Many drivers forget they are on because the dashboard light is small. Make a habit of checking the amber fog symbol whenever the fog thins out.
A Practical Rule
If you can clearly see the tail lights of the vehicle in front, the driver behind you can probably see yours. If those tail lights keep fading out or vanish altogether in dense fog, your rear fog lights are doing a useful job.
Front fog lamps follow the same use rule but do a different job. For the full picture on both sets, read our guide on when to use fog lights.
Why Rear Fog Lights Must Not Be Left On
Rear fog lights left on in clear conditions cause 2 problems: dazzle and brake-light masking.
- Dazzle: at normal following distances on a clear or wet night, a rear fog lamp is uncomfortably bright. It glares off a wet road and makes it harder for the driver behind to judge distance.
- Brake-light masking: a rear fog lamp is roughly as bright as a brake light, and on many cars it sits close to one. With the fog lamp on, the change in brightness when you brake is much smaller, so the driver behind is slower to notice you slowing down.
Rear fog lamps should also never be used as parking lights. If you stop at the roadside in fog, use your sidelights, and your hazard warning lights if you are causing an obstruction.
The Rear Fog Light Symbol
The rear fog light symbol is an amber (orange or yellow) warning light on the dashboard. It shows a lamp shape facing to the right with 3 straight horizontal lines coming out of it, crossed by a single wavy vertical line that represents fog. It lights whenever the rear fog lamp is on.
The front fog light symbol is green, faces the opposite way, and has lines angled downwards. The switch or stalk position for the rear fog lamp usually carries the same amber-style symbol. For a full side-by-side description of both symbols, how the switches work and what the colours mean, see our guide to the rear fog light symbol.
The tell-tale is part of the vehicle’s approved lighting installation, so if it stops working, get it fixed. It is the only reminder that the fog lamp is still on.
New Zealand Rules: Which Vehicles Need Rear Fog Lights
The Land Transport Rule: Vehicle Lighting 2004, administered by NZ Transport Agency Waka Kotahi (NZTA), covers fog lamps along with all other lamps. In general a rear fog lamp is optional in New Zealand, but where one is fitted it must meet the rules.
| Vehicle | Rear fog lamp required? |
|---|---|
| Car or van | Generally optional; many European-built vehicles have one fitted |
| Heavy vehicle | Generally optional; if fitted it must meet the rules and work |
| Agricultural tractor or self-propelled machine | Not generally required, but if fitted it must work |
| Agricultural trailer | Not generally required, but if fitted it must work |
| Any vehicle with a factory-fitted rear fog lamp | Keep it working; check NZTA guidance before removing or modifying factory lighting |
Where a rear fog lamp is fitted, it must be red. Lamps showing to the rear must be red, apart from a few exceptions such as indicators, number plate lamps and reversing lamps.
How Rear Fog Lights Are Fitted
New vehicles are fitted with rear fog lamps to the lighting installation rules they are approved under (for European vehicles, the UN ECE rules), so on a car, van or modern tractor the position is set at the factory. The practical points to know are:
| Requirement | What to check |
|---|---|
| Number | 1 or 2 |
| Position if only 1 fitted | On the right-hand side (the side nearest the centre of the road in left-hand traffic), or on the centre line |
| Position if 2 fitted | A matched pair, one each side |
| Distance from stop lamp | Kept well apart, so braking and fog lamp can be told apart |
| Colour | Red |
| Approval | A lamp meeting a recognised standard, such as an E or e mark for the rear fog function |
| Wiring | Must not light up when the brakes are applied |
| Tell-tale | A dashboard warning light that shows when the fog lamp is on |
The right-hand rule is why so many UK and Japanese-built cars sold in New Zealand have a single rear fog lamp on the right. New Zealand drives on the left, so the right-hand side is nearest the centre of the road, where the lamp is easiest to see for traffic behind and well away from the left-hand brake light. Vehicles built for right-hand traffic, such as some continental or US imports, sometimes have the single fog lamp on the left, which is worth checking.
Keeping the fog lamp away from the stop lamp is there for the brake-masking reason described above: if the 2 bright lamps were side by side, a driver could not tell braking from fog lamp.
On most cars the rear fog switch only works once dipped headlights (or front fog lamps) are on, which is how the European lighting installation rules are written. Some older vehicles and aftermarket installations do not do this.
Rear Fog Light Bulbs
Most rear fog lights with a replaceable bulb use a P21W (trade code 382), a 21W single-filament bulb on a BA15s bayonet base. Some modern clusters use a wedge bulb, and many newer cars use LEDs built into the lamp that cannot be changed separately.
| Bulb | Trade code | Base | Wattage | Where you find it |
|---|---|---|---|---|
| P21W | 382 | BA15s bayonet (pins level) | 21W | Most cars, vans, older tractors, standalone fog lamps |
| PR21W | None common | BAW15s bayonet (angled pins) | 21W | Some clusters that use a red-glass bulb behind a clear lens |
| W21W | 582 | W3x16d wedge | 21W | Some modern European clusters |
| P21W 24V | 241 | BA15s bayonet | 21W | Trucks, buses and 24V plant |
| Integrated LED | None | Built into the lamp | Typically a few watts | Many cars from the 2010s onwards, LED trailer lamps |
Always check the handbook or the old bulb before buying, because a bulb with the wrong pin layout will not lock into the holder. Our guide to P21W 382 bulbs covers the base, codes and replacement in more detail, and you can find replacement bulbs in our standard miniature bulbs range.
12V or 24V
Cars, vans and most tractors run on 12V. Trucks, many buses and some plant run on 24V. A 12V bulb in a 24V system blows almost immediately, and a 24V bulb in a 12V system glows weakly. Match the bulb or lamp to the vehicle voltage.
LED Rear Fog Lights
Complete LED rear fog lamps draw a small fraction of the current of a 21W bulb, last far longer, and cope with vibration better because there is no filament. They are a sensible choice for trailers, plant and tractors. Choose a complete lamp that carries an E-mark for the rear fog function (usually marked F on the lens). Browse our LED rear lamps for combination and standalone units.
Rear Fog Lights and the WoF or CoF
In New Zealand light vehicles are inspected for a Warrant of Fitness (WoF) and heavy vehicles for a Certificate of Fitness (CoF), to the standards in NZTA’s Vehicle Inspection Requirements Manual. Optional lamps such as fog lamps are checked too: if a rear fog lamp is fitted, it must work and meet the rules.
The common rear fog faults that cause trouble at an inspection are:
- Rear fog lamp not working.
- LED lamp with light sources out.
- Lens cracked or damaged so the light is affected.
- Lamp loose or likely to fall off.
- Fog lamp switch not working.
- Wrong colour (not red) or a lamp wired to come on with the brakes.
- Tell-tale not working.
A vehicle that fails can usually be rechecked once the fault is fixed, within the time the inspector gives. A blown bulb is the usual cause of a rear fog fault and the easiest to fix. A failed tell-tale is often a blown dashboard bulb or, on some cars, a symptom of a fog lamp circuit fault.
How to Replace a Rear Fog Light Bulb
On most cars and vans, replacing a rear fog light bulb takes 5 to 10 minutes with a screwdriver or trim tool.
- Switch on dipped headlights and the rear fog lamp, and confirm which lamp is out.
- Open the boot or tailgate and remove the trim panel or access cover behind the lamp. Bumper-mounted fog lamps are usually reached from underneath.
- Twist the bulb holder anticlockwise and pull it out.
- Push the P21W in slightly, twist anticlockwise and pull it out of the holder.
- Fit the new bulb (push in, twist clockwise until it locks) and refit the holder.
- Test the lamp and check the amber tell-tale lights before refitting the trim.
If the new bulb does not light, check the fuse, look for green corrosion in the holder, and check the earth. Where the fog lamp works but the tell-tale does not, the fault is on the dashboard side.
Rear Fog Lights on Tractors and Trailers
The rules for farm vehicles are not the same as for cars, and they catch people out.
Tractors
Agricultural vehicles in New Zealand have their own treatment under NZTA’s rules. A tractor used on the road at night needs headlamps, position lamps, rear lamps, stop lamps, indicators and number plate lighting, and amber warning lamps are required in various situations such as oversize or slow-moving operation. A rear fog lamp is not generally on that list, but most modern European tractors have one fitted. If it is fitted it must be red, must work, and should only be used in fog or similarly poor visibility. Many tractors do not need a WoF or CoF, but those that do have fitted lamps checked at inspection. For more on tractors specifically, see our guide to tractor fog lights.
Agricultural Trailers
Agricultural trailers and towed equipment used on the road at night need rear lamps, stop lamps, direction indicators and number plate lighting where a plate is fitted. A rear fog lamp is not generally required, but many farm trailers have one anyway, and it is useful on a trailer carting silage or grain on foggy autumn mornings (March to May in New Zealand). If one is fitted, it must be red, approved and wired so it does not light with the brakes.
Trailer Wiring
On a 7-pin 12N socket and on a 13-pin socket, the rear fog lamp feed is pin 2. A trailer fog lamp that does not work is usually a corroded pin, a broken earth, or a towing vehicle whose fog circuit is not connected through to the socket.
Wide Implements
When towed or mounted equipment hides the tractor’s front or rear lamps or reflectors, a lighting board is needed. If the board carries a rear fog lamp, place it on the right-hand side or centre, like a permanently fitted lamp.
Frequently asked questions
When should you use rear fog lights in New Zealand?
Only in fog, mist or other conditions where visibility is seriously reduced. Turn them off at all other times. Use dipped headlights with them, slow down and keep a safe distance.
Why does my car only have one rear fog light?
Many vehicles have a single rear fog lamp. In left-hand traffic the single lamp is usually on the right, keeping it away from the left-hand brake light and making it easiest to see for following traffic. Some cars fit 2 as a matched pair.
Is a rear fog light a WoF failure?
A fitted rear fog lamp that does not work, or that does not meet the rules, is a failure item at a WoF or CoF inspection, because fitted lamps, including optional ones, must work. Check with your inspector before removing factory-fitted lighting.
Can you get fined for using rear fog lights?
Using fog lights when visibility is not restricted, or using a lamp that dazzles other road users, is against the lighting rule, and NZ Police can issue an infringement notice for lighting offences. Check NZTA’s current guidance for the detail.
Can I use rear fog lights in heavy rain?
Generally no. Fog lamps are for fog and similar conditions where visibility is seriously restricted. In ordinary rain they dazzle drivers behind, reflect off the wet road and hide your brake lights, so leave them off and use dipped headlights.
