Position Lamp Not Working: What It Means at the NCT and How to Fix It
In this guide
A “position lamp not working” fault means one of your sidelights or tail lights is out. In Ireland a non-working lamp is a failure item at the NCT for cars and the CVRT for commercial vehicles, and a garage, tester or Garda may describe it by side: left (nearside) or right (offside). It is usually just a blown W5W (501) bulb and a 10-minute fix.
This guide explains what the fault means, how to find and change the bulb, what to check when a new bulb does not cure it, the rules on LED replacement bulbs, and what to do about the retest.
What “Position Lamp Not Working” Means
A position lamp is the official name for a sidelight (front, white) or tail light (rear, red). A test report or garage job sheet identifies the failed lamp using 3 pieces of information: front or rear, left or right, and the defect.
| Fault description | Which lamp on an Irish car | Usual bulb |
|---|---|---|
| Left (nearside) front position lamp not working | Front left sidelight, passenger side | W5W (501) |
| Right (offside) front position lamp not working | Front right sidelight, driver side | W5W (501) |
| Left (nearside) rear position lamp not working | Rear left tail light | P21/5W (380), R5W (207) or W5W |
| Right (offside) rear position lamp not working | Rear right tail light | P21/5W (380), R5W (207) or W5W |
Left and right are always judged from the driver’s seat facing forwards. Ireland drives on the left, so the left (nearside) is the side nearest the kerb and the right (offside) is nearest the centre of the road. They do not change on a left-hand-drive car, which matters on imported vehicles.
For background on the lamps themselves, see our guide to position lamps.
Is a Position Lamp Not Working a Test Fail in Ireland
Yes. Cars take the NCT and commercial vehicles take the CVRT, both run by the RSA, and RSA guidance is that fitted lamps must work. A position lamp that is missing or not working is a failure item at both tests. Front position lamps must show white and rear position lamps red (RSA lighting colour guidance, citing the Road Traffic (Lighting of Vehicles) Regulations 1963), and a red light to the front or white light to the rear is not allowed.
Things that commonly cause a lighting fail on position lamps:
- Lamp missing or not working
- LED lamp with a large share of its light sources out
- Cracked or defective lens, or water inside the lamp
- Wrong colour (a blue-tinted front sidelight, or a white light showing to the rear)
- Lamp loose or insecure
At the CVRT, defects are graded minor, major or dangerous, and a failed vehicle must be retested within 21 days. Check cvrt.ie for the CVRT and ncts.ie for the NCT retest arrangements and fees, as these can change.
A position lamp fault is not usually treated as dangerous, but position lamps are needed during lighting-up hours (half an hour after sunset to half an hour before sunrise). Using a vehicle that is not equipped with the prescribed lamps can lead to a €60 fixed charge, so fix it before you drive in the dark.
Front Position Lamp Not Working: Change the Bulb
On most cars the front position lamp uses a W5W (501) capless wedge bulb, fitted in a small holder in the back of the headlamp unit. A few use an R5W (207) bayonet bulb or an H6W (434) offset-pin bulb. Check the handbook or pull the old bulb to be sure.
- Confirm which lamp: switch the sidelights on and walk round the car. Front left is nearside, front right is offside.
- Open the bonnet: find the back of the headlamp on that side. The sidelight holder is the small one, often beside the larger headlamp bulb cover. On some cars you reach it through the wheel arch liner or need to remove the air box or battery on one side.
- Remove the holder: most twist a quarter turn anticlockwise and pull out. Some just pull out.
- Remove the bulb: a W5W pulls straight out of the holder. Do not twist it.
- Fit the new bulb: push the new W5W straight in. Wear gloves or use a cloth if the glass is hot or sharp-edged.
- Test before refitting: switch the sidelights on with the holder hanging loose to check it works, then refit and check again.
Our guide to W5W 501 bulbs has more on the base and codes, and you can order replacements from our standard miniature bulbs range. It is worth changing both sides at once, because the other bulb is the same age.
Rear Position Lamp Not Working
The rear position lamp is the tail light. Many cars use a P21/5W (380) twin-filament bulb that does both tail and brake, so check both functions:
- Tail light out but brake light works: the 5W filament has broken. Replace the P21/5W.
- Tail light and brake light both out on that side: the bulb has failed completely, or the holder or earth is faulty.
- Tail light glows brightly or brake light is dim: a bulb forced in the wrong way round in a worn holder, or a poor earth letting current find another path.
Rear bulbs are reached from inside the boot, behind a trim panel or cover, or by unbolting the rear cluster (usually 2 or 3 nuts or screws). The P21/5W has offset pins so it only fits one way. See our P21/5W 380 bulbs guide for how to tell it from a single-filament bulb.
Some cars use LED rear lamps with no replaceable bulb. If an LED tail light is out, the lamp unit (or its LED board) usually needs replacing. Partial LED failure can also be picked up at a test, so don’t leave a half-dead LED tail light.
New Bulb and Still Not Working
If a new bulb does not cure it, work through these checks in order.
1. Holder Corrosion
Green or white corrosion on the contacts is common where water has got into the headlamp or cluster, and Irish weather gives it plenty of chances. Clean the contacts with fine abrasive paper or a small brush and contact cleaner, bend them gently so they press firmly on the bulb, and add a smear of dielectric grease. If the holder is melted or the contacts have rotted away, replace the holder.
2. Fuse
Many cars fuse the sidelights by side (left side lamps on one fuse, right side on another) or all together. If both front and rear on one side are out, or all of them, the fuse is the first thing to check. The fuse box lid or handbook shows which one. Replace it with the same rating; if it blows again, there is a short circuit to find. Spares are in our fuses and fuse holders.
3. Earth
Use a test lamp or multimeter across the 2 holder contacts with the sidelights on. If there is 12V from the feed to bare metal but not across the holder, the earth is bad. Trace the earth wire (usually black or brown) to its bolt on the body and clean it to bare metal.
4. Wiring and Plugs
Check the plug at the back of the headlamp or cluster for corrosion and broken pins. Rear lamp wiring often breaks in the flexible gaiter between the body and the tailgate. On tractors and trailers, look for chafed looms on the chassis, rodent damage and corroded trailer plugs.
5. Light Switch or Body Control Module
On modern cars the sidelights are often switched through a body control module, and some monitor each bulb. If no lamps work and the fuses are good, a light switch or module fault is possible, and a diagnostic scan is the next step.
LED Sidelight Bulbs and CANbus Warnings
LED W5W bulbs are a popular swap, but they come with 2 catches.
CANbus Bulb Warnings
Many modern cars check the current each bulb draws. An LED bulb draws so little that the car decides the bulb has blown, shows a warning, or pulses the power so the LED flickers. A CANbus-compatible LED bulb has built-in electronics to avoid this. Some cars can be recoded to accept LEDs. If the warning still appears, refit a standard filament bulb.
Are LED Sidelight Bulbs Legal in Ireland
Strictly, most LED replacement bulbs are not legal in a lamp that was type approved for a filament bulb, because the lamp is no longer in its approved form. Lamps are approved with a specific light source, and most retrofit LED bulbs are not approved as a substitute. A small number of LED substitute (LEDr) bulbs have been approved for specific uses under UN Regulation 37, and they are marked accordingly, but most marketplace LED bulbs are sold “for off-road use”.
RSA guidance says LED bulbs are legal only if type-approved, fitted to a compatible vehicle, and not dazzling, and its NCT failure points for unapproved or incompatible LED kits are written mainly with headlamps in mind. For sidelights, a tester will look at whether the lamp works, its colour and its brightness. A strongly blue LED, or one so dim or so bright it is clearly wrong, is likely to be picked up. The safest choice for the NCT is a standard W5W filament bulb, or an approved LED lamp carrying an E or e mark.
Cost and Getting the Retest
A position lamp fail is one of the cheapest test fails to fix. A W5W or P21/5W bulb costs a few euro, and most people can fit one at the roadside. Some cars need more work to reach the front sidelight (removing a wheel arch liner, battery or headlamp), which is why garages charge more than the bulb on those models.
For the retest:
- Book the NCT retest through ncts.ie and check the current time limit and any fee before you go.
- For a CVRT fail, the vehicle must be retested within 21 days.
- Keep the test report: it lists the failed items, so you can confirm the right lamp has been fixed.
- Remember that using a car without a valid NCT certificate carries a €60 fixed charge and 3 penalty points, so don’t let a cheap bulb fault drag on.
Fix it before the test if you can: walk round with the sidelights, dipped beam and hazards on the week before your NCT. Replacement position lamps for trailers, tractors and older vehicles are in our position lamps range, with free delivery to Ireland on orders over €150.
Frequently asked questions
What does nearside front position lamp not working mean?
Your front left sidelight (the passenger side on an Irish car) is not working. It is usually a blown W5W (501) bulb in the back of the left headlamp.
What does offside front position lamp not working mean?
Your front right sidelight (the driver side on an Irish car) is not working. Check the W5W bulb in the back of the right headlamp, then the holder and fuse.
Is a rear position lamp not working an NCT fail?
Yes. A missing or non-working rear position lamp (tail light) is a failure item at the NCT, and at the CVRT for commercial vehicles. A partly failed LED tail light can also be picked up.
Will an LED sidelight bulb pass the NCT?
Often, if it works, is white (not strongly blue) and is not obviously too dim or bright. Most LED retrofit bulbs are not type approved, though, and RSA guidance says LED bulbs are legal only if type-approved and compatible. They can also cause bulb warnings on CANbus cars. A standard W5W is the safest option.
Can I drive with a position lamp not working?
Position lamps are needed during lighting-up hours, and using a vehicle not equipped with the prescribed lamps can lead to a €60 fixed charge from the Gardaí. Replace the bulb before driving in the dark.
