W124/W201 turn signals not working? Check the turn signal relay

The fault pattern is unmistakable: the turn signal stalk engages, nothing happens in the instrument cluster, and the familiar clicking stays silent. In some vehicles it affects only the hazard warning system, while in others the wiper interval fails at the same time – a connection that puzzles many owners, since turn signals and wipers seem to have nothing to do with each other at first glance. In the W201, W124, W126, and W202 model series, however, these functions run through relays in the central relay holder, and a single component handles several circuits. Before removing the steering column switch, it's therefore worth taking a structured look at the chain of bulb – ground – fuse – relay.

Symptoms

This overview helps classify the fault pattern before you order parts:

Symptom	Likely cause
Turn signals left and right not working, no clicking audible	Relay no longer switching through – classic failure pattern
Hazard warning dead, turn signals via the steering column switch still work	Individual output or contact set within the relay has failed
Turn signals cut out intermittently, work again after cooling down	Cold solder joints or shifting contact points in the relay
Wiper interval not working, continuous settings still run	Interval section of the combined turn signal and wiper relay affected
Not to be confused with: One side blinks noticeably faster than the other	Faulty bulb, corroded socket, or poor ground at the light – not the relay
Not to be confused with: Alongside the turn signal, other electrical functions also fail (W126, W201)	First rule out the overvoltage protection relay – see Checking the overvoltage protection relay
Not to be confused with: Same fault pattern, but on the W140	There a dedicated control unit takes over – see Check W140 turn signal unit

Causes

A turn signal relay switches a load on every turn – over the decades, several hundred thousand times. This is exactly where the components fail, in three recurring ways.

First, the solder joints. Every switching cycle produces a small temperature swing at the connector pins, the material works, and after thirty to forty years the solder joint cracks hairline-fine. Such faults show up intermittently at first: the turn signal fails on a warm summer day and works fine again the next morning.

Second, the internal contacts. They slowly burn away from the switching spark and oxidize during the long periods of disuse typical of classics. Contact resistance rises until the relay engages but no longer lets a clean current through.

Third, the environment. The relay holder isn't a sealed chamber: moisture and condensation make plug contacts turn green with verdigris. In that case it's not even the relay's fault – one more reason to measure before replacing parts.

Testing it yourself

The sequence deliberately starts with what costs nothing:

1. Check bulbs and sockets. Inspect all turn signal lights all round, including the side repeaters and the indicator light in the instrument cluster. Blackened bulbs, loose bases, and green-corroded sockets are by far the most common cause – and the cheapest to fix. Check ground connections at the lights too.
2. Check fuses. The old torpedo-style fuses often crack invisibly at the cap – a visual check isn't always enough. Pull them out, test with a continuity tester, clean corroded holders.
3. Reseat the relay. Pull the relay out, check the plug pins and socket for corrosion, treat with contact cleaner, and plug it firmly back in. This often fixes the fault – a loose contact causes the same intermittent behavior as a faulty component.
4. Measure voltage at the socket. Use a multimeter to check whether battery voltage is present at the relay socket and whether the ground is clean. If no voltage is present, the path continues via fuse, ignition-switched positive, and connector – in that case a new relay is money wasted.
5. Do a swap test. If voltage is present but the function still fails, fit a known-good relay of the same part number. If the turn signals, hazard warning, and interval then work again, the diagnosis is confirmed.

Solution

If the suspicion is confirmed, the relay is replaced – in practice these sealed components aren't repaired. We supply the genuine relay for this with the Mercedes part number A2018210047, which is listed in the product data as the turn signal or wiper relay for W201, W124, W126, and W202. The condition is stated as used, and the scope of delivery matches the images exactly. Installation is a plug connection, no special tools needed.

You'll find more switching relays and control units for your classic in our category Relays, the complete range for the model series under W124. If other electrical functions fail alongside the turn signal, first check the article on the overvoltage protection relay – in the event of a fault, this component knocks out several circuits at once.

Compatible vehicles

Model series	Note
W201	Fits according to product data.
W124	Fits according to product data.
W126	Fits according to product data; for special equipment, check beforehand.
W202	Fits according to product data.
Other model series	Not documented for this part – please ask before ordering so we can verify it.

FAQ

How can I tell whether the turn signal relay or just a bulb is faulty?

The difference lies in the pattern. If one side blinks noticeably fast, or only a single light fails, it's almost always a bulb, its socket, or the ground point at the light. If instead both sides stay silent, the familiar clicking is missing, and the hazard warning switch doesn't respond either, the path leads to the relay.

Why do the turn signals and wiper interval fail at the same time?

Because one relay handles several circuits. The part numbered A2018210047 is listed in the product data as the turn signal or wiper relay. If the internal control fails, functions that seem to have nothing to do with each other disappear together as a result.

Am I allowed to keep driving with a faulty turn signal relay?

Turn signals and hazard warning lights are legally required equipment. Without working turn signals the vehicle isn't roadworthy, and at the periodic inspection the failure results in a significant defect. So the replacement shouldn't wait.

Does part number A2018210047 fit my vehicle?

The product data confirms the fit for W201, W124, W126, and W202. Because different equipment levels were fitted across the model years, we check the fit against your chassis number and model year before you order, free of charge.

What does the turn signal relay A2018210047 cost, and is it in stock?

The genuine relay with part number A2018210047 costs 29.00 € with us. It's available in stock and shipped in the scope of delivery shown; the product data states the condition as used.

KFZTeile-Thot is a specialist for tested and refurbished Mercedes parts with its own test benches. Every part that leaves our warehouse has been personally tested beforehand – that's the difference to anonymous used parts. Over 1,000 eBay reviews (almost exclusively positive) show that this approach works. Not sure about the fit, or want to discuss a fault pattern beforehand? Call us on 0179 8991069 (Mon–Fri 8 am–6 pm) or write to us via our contact form – we'll check the fit against your chassis number free of charge.