Key spinning freely? W123/W126 ignition lock, petrol

On the 123 and 126 petrol models, the trouble starts harmlessly: the key goes into the lock a little more stiffly, you jiggle the steering wheel briefly, and the car starts. Months later it sticks in one position – or spins with no resistance at all. The electrical variant is more unpleasant: the engine cuts out while driving because the ignition/starter switch briefly drops terminal 15. On a petrol engine it then stalls immediately – which is why the ignition system is often suspected, even though the fault is in the steering lock.

0160-family steering-lock casting with lock cylinder, locking bolt, and 7-pin ignition/starter switch – petrol version for W123 and W126.

Symptoms

Symptom	Likely cause
Key spins with no resistance, nothing switches	Connection between lock cylinder and ignition/starter switch broken
Key turns only with difficulty or not at all	Worn tumblers in the lock cylinder, hardened lubricant
Ignition briefly cuts out while driving, the engine stalls	Burnt contacts on terminal 15 in the ignition/starter switch
Starter does not respond even though the key is in the start position	Terminal 50 no longer gets a clean contact in the switch
Steering stays locked or no longer locks	Sticking locking bolt in the steering-lock housing, often with the wheels turned
Starter cranks strongly, but the engine still won't start after standing	Not the lock: on the K-Jetronic petrol engine, the fuel accumulator does not hold residual pressure – the procedure is shown in W116/W126 cranks but won't start
Your vehicle is a 190 or a 124	Different design: that generation carries the 1900.01 marking – matching guide: W124/W201 ignition lock faulty

Causes

The steering lock of the 123 and 126 model series is a die-cast housing with three assemblies that age differently: at the front, the lock cylinder with spring-loaded tumblers; behind it, the locking bolt that locks the steering column when the key is removed; and at the rear end, the round, 7-pin ignition/starter switch with permanent positive (terminal 30), operating voltage (terminal 15), starter control current (terminal 50), and parking lights (P30).

Mechanically the equation is simple: after four decades, the key bit and tumblers have worn down, the springs have fatigued, the grease has hardened – penetrating oil buys a few months of peace, no more. Electrically it hits the ignition/starter switch: every start puts the full control current through its contacts, and on the petrol engine the entire ignition system hangs off terminal 15. Burnt contact surfaces show up intermittently – the ignition briefly cuts out over a speed bump, and after turning the key again everything runs fine. Anyone who replaces the ignition coil or wiring harness here is taking the more expensive route.

Checking it yourself

1. Test with a spare key – costs nothing and clarifies the most. If the lock runs noticeably more smoothly with the rarely-used spare key, your everyday key is worn. If it stays stiff, the wear is in the cylinder.
2. Relieve load on the steering wheel – move it slightly back and forth while turning the key. If it then works, only the locking bolt is under preload – the most common false alarm with the wheels turned.
3. Separate mechanics from electrics – if the key turns cleanly through all positions without the warning lights or starter responding, the fault is in the electrical part; if it noticeably sticks, it is in the mechanics.
4. Check the connector and measure the terminals – remove the steering column trim, unplug the connector at the back of the switch: bent or scorched contact pins explain intermittent faults that would otherwise be blamed on the cylinder. If permanent positive is present at terminal 30, but voltage is missing at terminal 15 in the run position or at terminal 50 when attempting to start, the switch has failed. Wiggle the key while doing this – if the reading jumps, the contact surfaces are burnt.

Solution

A worn-out lock cylinder cannot be readjusted, and repairing a burnt ignition/starter switch with the lock still installed is not worthwhile. The clean solution is to replace it with a tested genuine part: Ignition lock with steering lock, part number A1234620730, petrol version for W123 and W126. With matching key it costs 219,00 €, without key 159,00 €. Every unit is personally tested – the key turns cleanly through all positions and the mechanism engages correctly.

Two points before installation. First, identification: the housing carries the marking of the 0160 family from the W123/W126 era – compare the design, connector layout, and, if present, the part number of your old part 1:1 with the product photos. Second, the locking: the lock has its own lock combination and opens neither the doors nor the trunk. It is installed on the steering column tube under the steering column trim.

Tested, in stock: steering locks A1234620730

All four units carry the same part number and stamping and differ only in whether a key is included. Current stock: W123, W126, Locks & door handles.

Compatible vehicles

Documented assignment per product listing – the gasoline version of the 0160 family is specified:

Model series	Body style	Engine	Models per product listing
W123 (approx. 1976–1986)	Sedan	Gasoline	200, 230, 230 E, 250, 280, 280 E
C123	Coupe	Gasoline	Gasoline models in the model series
S123	T-model (station wagon)	Gasoline	Gasoline models in the model series
W126 (until approx. 09/1989)	Sedan	Gasoline	SE / SEL
C126 (until approx. 09/1989)	Coupe	Gasoline	SEC

Not to be confused with: This lock does not fit diesel models – they require the version with two vacuum ports, described in the guide W123/W126 diesel ignition lock defective. Also not compatible: W201/W124 (stamping 1900.01), W126 from approx. 10/1989 as well as W113, early W108/W111 and W110. Not sure? Send the chassis number and model year via the contact form send – we check the fit free of charge.

FAQ

Does this ignition lock also fit a W123 or W126 diesel?

No. Diesel models need the version with two vacuum ports for engine shutoff. A1234620730 is the gasoline version; for diesel, steering lock A1234622830 applies.

How can I tell if my steering lock belongs to the 0160 family?

By the housing stamping: the design from the W123/W126 era carries the 0160 family stamping, while the newer generation for W201 and W124 has the 1900.01 stamping. Compare the stamping, design, and connector layout with the product photos.

I no longer have a key – how do I get a matching one?

Three options: Mercedes can produce one from the lock number (via a dealership, proof required), specialist locksmiths can read the lock code from the cylinder, or you install a new lock cylinder – key blanks are freely available.

Does the included key also open the doors and trunk?

No. The lock comes with its own locking system. Anyone who wants to keep one key for everything can have the cylinder re-keyed or transfer the cylinder from the old part.

What does the ignition lock for the W123/W126 gasoline cost and is it available?

With key 219,00 Euro, without key 159,00 Euro. At the time of publication, four tested steering locks A1234620730 are in stock. If a product page shows sold out, it's worth checking the other units.

Further reading: W123/W126 diesel ignition lock defective? Replacing the steering lock – the guide for the diesel version with vacuum shutoff.

KFZTeile-Thot is a specialist for tested and refurbished Mercedes parts with our own test benches and has over 1,000 positive eBay reviews. We have ignition locks, lock cylinders and many other genuine parts for W123 and W126 tested and in stock. Questions about fit? Call us: 0179 8991069 (Mon–Fri 8 am–6 pm) – or use our contact form.