W123 Ignition Switch and Lock

How to Replace a Mercedes W123 Ignition Switch

This blog will focus on the removal and/or replacement of the later model, (from chassis No. 208267) W123 ignition switch (7 pin) and lock housing assembly and lock. Note: Chassis 208266 and earlier requires a different ignition switch (8 pin) assembly.

Always check your VIN for the chassis number prior to ordering any parts. The chassis number is the last 6 digits of the VIN.

TIP: Before you start, I recommend taking photos each step of the way so you remember exactly how everything goes back together. Loose parts can accumulate quickly and losing track of what went where, is easy to do.

STEP 1
DISCONNECT THE BATTERY! This is a good habit to get into when undertaking numerous jobs on your car.

STEP 2
Remove steering wheel center emblem. Gently pry plastic star ornament from center of steering wheel. Use a small trim removal tool. Note: Be careful not to scratch the back on removal as it will remove the blackout and or silver star coating. This plastic is clear and and simply panted on one side.

STEP 3 
Remove steering wheel bolt using a 10mm hex socket. DO NOT use steering wheel lock to hold the steering wheel while attempting to loosen the bolt. Doing so can result in damaging the lock mechanism. To keep the lock from engaging, turn key to position "I". It may be necessary to have another person holding the steering wheel while a breaker bar with an 8 in. extension. There is no need to remove the horn pad for this procedure. An impact wrench can also be used for quick and easy removal.

STEP 4
Remove steering wheel. Before doing so however, mark steering wheel and hub with pencil or marker to insure wheel is returned to the centered position.

STEP 5-1
Remove gauge cluster. Withdraw by means of Mercedes tool No.140 589 0233 00 shown, or by reaching up from under the dash and pressing it out from the back (steps for removal of the lower dash panel next). Pulling the cluster out more than a few inches will not be possible until the speedometer cable has been removed. Once speedometer cable has been removed, the main electrical, clock, two light bulbs and the oil pressure line will also need to be removed.

STEP 5-2
Remove wiring from cluster as shown.

STEP 5-3
Remove remaining wiring as shown. Main connector, oil pressure line and speedometer plug.

STEP 6
Remove lower dash panelling. Remove the three screws holding the panel to the facia along with the gray plastic locking "screw" from near the emergency brake pedal. 

STEP 7
Remove the two vacuum lines from ignition housing (diesel models only). Mark lines to be sure they are returned to the correct port on reinstallation.

STEP 8
Remove chrome trim ring from ignition key tumbler housing on dashboard. Remove very gently with small plastic trim removal tool. The three retaining clips can only handle a few removals before they break off, rendering the ring useless. Photo shows trim ring removed.

STEP 9
Remove lock tumbler by turning key clockwise to the "accessory" position. Next, insert a strong wire such as a paperclip or similar sized wire. This wire will act as a secondary "key". It is very helpful to file a 45º angle on the tip of this wire for easy of insertion. The wire should be no shorter than 3 inches for ease of use. Insert wire as shown until it stops. Next, loosen and remove the black tumbler housing by turning counter clockwise until fully loose. NOTE: If the tumbler housing does not turn, the wire has not been properly inserted. At this stage, the key, tumbler and tumbler cover can be removed as a unit. To separate the tumbler from the housing and key, hold the back of the tumbler assembly with your finger and turn the key to position "1" and with draw key. NOTE: The wire "key" must remain in place during the entire process until the tumbler, etc., has been removed. Reinstallation is the revers of this process.

LOCK TUMBLER REPLACEMENT ONLY
If you are just in need of replacing the lock tumbler, this step, "STEP 9" would be the only step necessary for the job. NOTE: If the lock ever begins to not function smoothly, replace it at once. Many older Mercedes end up having to have the locks drilled out.

Image below shows tumbler and assembly removed

STEP 10
Remove ignition switch plug. Gently wiggle it loose. It is tight up against air ducts and the steering column brace. Although there are finger grips as the photo shows, it is nonetheless firmly seated.

STEP 11
Remove seatbelt warning buzzer plug (USA models only). This plug is located on the under side of the ignition lock housing and can only be accessed from under the dash.

STEP 12
Loosen steering column ignition housing clamp bolt. 5-6 full turns should be sufficient to withdraw lock housing. 

STEP 13
Depress ignition lock housing anti-theft "button". I used a nail punch to depress the button, but any similar sized object will suffice. It does not require any force and will only depress about 1 or 2mm. While depressing the "button" wiggle the ignition lock housing outward from the column sleeve. Once the lock housing has been moved outward but a few millimeters, the anti-theft button can be released. Continue to withdraw the lock housing in the out ward and upward direction. The housing will ultimately come out through the cluster gauge opening. NOTE: Do not force! It is a snug fit and the dash board can very easily be damaged around the ignition key area. Remember the dashboard material on these older cars is no longer very forgiving and will crack and crumble very easily.

STEP 14
Remove the three recessed ignition switch retaining screws and withdraw switch. The new ignition switch has a tab on one side that will align with a groove on the housing to avoid improper installation. 

While this process may appear overly complicated for such a simple part, it is unfortunately necessary. Consider however, it probably won't need to be done again for another 30+ years.

Now, simply reverse the process to complete the job.