W140/R129 turn signals & wipers acting up? Check combination relay N10
The turn signal stays dark, the hazard lights no longer tick, and the windshield wiper works on and off: with this symptom, many owners of an S-Class W140 or an R129 SL first look in three different places. In fact, these functions all run through one shared component, the combination relay N10. In this guide you will learn how to narrow down the fault, what you can check yourself beforehand, and which part number you need.
Symptoms
| Symptom | Likely cause |
|---|---|
| Turn signals left and right not working, hazard warning lights dead as well | Combination relay N10 defective or fuse blown |
| Turn signal cuts out sporadically, especially after jolts | Aged solder joints in the combination relay or poor contact at the socket |
| Windshield wiper runs erratically or stops, plus turn signal problems | Combination relay N10, since it controls both functions |
| Turn signal flashes twice as fast on one side | Usually a defective bulb or socket – not the relay |
| US-spec vehicle with the same symptoms | Different relay variant – see Guide to the combination relay of the US version |
| Only the turn signal is affected, the wiper works normally | Also check the turn signal switch and hazard warning switch – more in the W140 turn signals & hazard lights guide |
Causes
The combination relay N10 combines several switching functions in one housing: the flasher unit for the turn signals and hazard lights as well as the control of the windshield wiper. According to the product data, the A1408207126 version also includes trailer mode. The relay is at work on every drive, every time you signal and every wiper interval.
After decades in service, typical signs of aging appear: solder joints on the circuit board crack from temperature changes and vibration, relay contacts wear from arcing, and the contacts at the socket oxidize. The result is sporadic dropouts at first, and later the function fails completely. Because several functions run through one component, the fault often seems more confusing than it actually is.
Testing it yourself
- Check the bulbs: Check all turn signal bulbs at the front, rear and sides. A defective bulb changes the flashing rate and is the cheapest source of the fault.
- Check the fuses: Use the fuse assignment chart in the fuse box to check the fuses for the turn signals and the windshield wiper.
- Test the functions against each other: Switch on the left turn signal, the right turn signal and the hazard lights, and test all wiper speeds. If several functions fail together, that points strongly to the combination relay.
- Check the plug contacts: With the ignition off, pull out the relay and inspect the contacts and the socket. Carefully clean any corrosion or straighten bent contacts.
- Counter-test with a tested relay: If everything works with an intact combination relay of the same part number, the cause is clear.
Solution
Once the combination relay is confirmed as the cause, replacing it with a tested genuine part is the most sensible solution. Before ordering, compare the part number on your old relay: for the ECE version with trailer mode, that is A1408207126. We offer this genuine used part from Mercedes-Benz for 169,00 € . More relays and control units can be found in our category Mercedes relays & control units as well as under Spare parts for the W140.
Mercedes combination relay N10 A1408207126
W140 · C140 · R129 SL – turn signals, hazard lights, windshield wiper (ECE, with trailer mode)
169,00 €
View productCompatible vehicles
| Model series | Model | Note |
|---|---|---|
| W140 | S-Class sedan | ECE version with trailer mode |
| C140 | S-Class coupe | ECE version with trailer mode |
| R129 | SL | ECE version with trailer mode |
What matters is always the part number on your installed relay. If in doubt, send us a photo of the old relay or your VIN (chassis number) – we will check the fit for you.
FAQ
How can I tell that combination relay N10 is faulty?
Typically, several functions fail at the same time or work erratically: turn signals and hazard lights stay dark, stop ticking or cut out, and the windshield wiper also behaves unsteadily. If only a single turn signal side fails, however, the cause is usually the bulb or its socket.
Does A1408207126 also fit a US-spec W140?
Check the part number of your old relay. According to the product data, A1408207126 is the ECE version with trailer mode. There is a separate part number for the US version, which we cover in a separate guide.
Why does the turn signal suddenly flash twice as fast?
An increased flashing rate usually indicates that a bulb in the turn signal circuit has failed or has poor contact. First check all turn signal bulbs on the affected side before replacing the relay.
Can I replace the combination relay myself?
Yes, the relay simply plugs in. Switch off the ignition, pull the old relay straight out, compare the part number and the connector layout, and plug in the new relay. Then test the left and right turn signals, the hazard lights and all wiper speeds.
How much does the combination relay N10 A1408207126 cost?
The tested genuine used part A1408207126 costs 169,00 € at KFZTeile-Thot. You can see the current stock on the product page.
KFZTeile-Thot is a specialist business for tested and refurbished Mercedes parts with its own test benches and has over 1,000 positive eBay reviews. Not sure whether A1408207126 fits your car? Call us at +49 179 8991069 (Mon–Fri 8 am–6 pm) or write to us via the contact form.