DIY Ignition Switch/Steering Lock R&R W124 - PeachParts Mercedes-Benz Forum

Jeremy5848 · #1 07-19-2010, 06:46 PM

This is based on my recent adventure changing the glow/starter switch in my 1987 300D Turbo (W124, OM603). Removal of the steering lock and the glow/starter switch is covered in detail with pictures. I have assumed that you can get your key into the lock and turn it to "position 1." If you have lock cylinder problems, this thread will not help you.

It took a good while to find the instructions in the FSM because the ignition switch is considered part of the steering lock mechanism, so it was placed in the "Body" section under "Steering," where it is section 46-8010 (5 pages), "Removing and installing the steering lock complete."

Although the FSM says in this section (bottom of the fourth page) that the ignition switch can be removed with the steering lock still in the car, I do not advise it. It's easier to remove the steering lock and switch as a unit.

You do not have to remove the steering wheel although access is a little easier when it is out. If you do remove the steering wheel, be careful not to damage the combination switch or the cruise control switch as they no longer have the wheel to hide behind. The airbag is held on by T30 Torx screws (access through two holes in back of the steering wheel). The steering wheel is held on by a 10 mm Allen screw that is very tight and also has blue Loc-tite ® on it. Make sure the car's wheels are turned dead straight ahead and note the position of the steering wheel so you get it back in the same place.

First step in all cases is to disconnect the negative battery cable and make sure it can't accidentally touch the battery post.

If you choose to remove the steering wheel and airbag, you must go into the front passenger footwell and unplug the red airbag connector.

Now unscrew the two Torx screws, lift off the airbag, and unplug its little red connector. Put the airbag away in a safe place. Loosen the 10 mm screw in the center of the steering wheel. Use the steering lock to keep the wheel from turning (FSM advice) and use a good-quality Allen socket with a short extension and a long bar. With the screw out, the steering wheel will pull off easily. While you have the steering wheel off, check and clean the contact rings in the wheel and the carbon brushes in the steering column. Put the steering wheel away in a safe place.

Now remove the driver's lower dash panel. You will then be able to see the steering lock. The ignition switch is all the way forward on the assembly and very hard to see. Put the key in the lock, turn it to position 1, and use the home-made wire tool described in FSM 46-8010 to remove the lock cylinder. Note the diagonals cut on the tips of the wire -- they are critical. Put the key, lock cylinder, and wire tool away in a safe place just as you removed them from the steering lock assembly. From this point on, do not turn anything in the lock assembly.

The next picture was taken from underneath.

Pull off the plug at the back of the glow/starter switch. There isn't a lot of room back there but you should be able to get the plug loose and out of the way. If you have a later model W124, there will be a transmission lock cable that you will have to remove. FSM 46-8010 shows it but my car doesn't have one so it's not in my picture. Also disconnect the connector(s) for the warning buzzer. (This is the alarm that tells you that you have left the key in the ignition.)

The FSM now wants you to remove the vacuum hoses that shut off the engine in diesel models. However, I found them really hard to see, much less touch, and decided to loosen the steering clamp first. Therefore, I used an Allen wrench (I think it's 4 mm) to loosen the clamp (you don't need to remove the screw). Press in the locking pin using a small screwdriver or pin punch and twist the steering lock while pulling it partly out of the clamp so you can get at the two plastic vacuum hoses. Pull the rubber connectors off of the vacuum switch, making sure you remember which line goes where. The brown hose goes outboard, the brown/blue hose goes inboard. The rubber jumpers are not color coded.

With all that stuff off, the lock assembly is ready to come out. I had always wondered why the climate control air box had a rubber section. I now found out why.

The steering lock mechanism is so long that to get it out of the jacket tube you must push it well into the air box. You don't need to remove the rubber piece but it requires some pushing and wiggling and there is barely enough room to get it out. FSM never mentions this, of course. Once you get the mechanism out, you can lay it on your work bench and it looks like this picture. Resist any urges to fiddle with the innards of the mechanism.

Now you can remove the glow/starter switch from the lock assembly. Hold the lock (it's convenient to put it in a vise using a rag to prevent scratching) and remove three slotted screws. The switch will lift out and should be covered with white grease. Scrape off some of the grease to put on the new switch, then toss the old one. One final warning: the FSM says that if you try to turn the steering lock mechanism with the switch removed, a detent in the lock mechanism locks in such away that it cannot be unlocked. Take heed and do not fool around!

Notice that the switch has two rounded "corners" and one square corner as well as a locating protrusion that fits into a matching notch in the steering lock. The new switch must go in just as the old one came out.

Remember that the old switch came out in "position 1" so the new one must be in the same position to go in. The picture shows the "face" of the switch, the part that goes into the steering lock assembly.

With the switch turned to "position 1," apply the white grease you removed from the old switch and put the new switch into the lock such that the protrusion goes into the notch. Insert and tighten the three slotted screws. Leave the mechanism in "position 1."

Now wiggle and squeeze the lock mechanism back into the jacket tube, compressing the locking pin with your fingers until it goes into the tube. Reconnect the vacuum lines and push/twist the mechanism until the locking pin pops out of its hole. Notice that there is some rotational play in the lock assembly. Make sure that the locking pin does not bind in its hole and also that the lock is lined up so that the escutcheon will go over the lock cylinder when you put the lower dash cover back on. I found that "tilted down a little" is the preferred way but I had to remove the lower panel again to get it right.

With the steering lock back in place, tighten the clamp, reconnect the buzzer connector(s), reattach the cable to the transmission if you have one, and put the big plug onto the new glow/starter switch. Notice that the lock assembly is still in "position 1."

Now retrieve the cylinder lock with the key and special wire tool still in it, and carefully put the cylinder back just the way you took it out. Once you are sure you have the cylinder all the way in, remove the special wire tool. While holding/pushing the lock cylinder in with one hand, try turning the key a little to see if it "feels right." If it does, see if the key will turn to "position 0" and come out.

The lock cylinder now should be firmly in place and you should not be able to pull it back out. If you can, you didn't push it in far enough. There's a little detent that must line up between the lock cylinder and the steering lock mechanism. I had a hard time getting it to engage the first time but with some patient wiggling it went all the way in and the lock locked in place.

Once the lock is firmly seated, you should be able to insert the key and turn it through its various positions including "start," which should be spring-loaded and should have a non-repeat function (you must turn the lock all the way off before it will go into "start" again).

With that, the hard parts are done. You still have to put the lower panel back and reattach the steering wheel and airbag. Wire brush the big screw and use fresh blue Loc-tite ®. The little red airbag plug must audibly snap back in place (it has a built-in short-circuit link that you are pushing out of the way -- see FSM 91-660 for details). Plug the red connector in the passenger footwell back together and replace the floor panels. Now reattach the battery negative cable.

With everything back together, you should be able to insert the key and start the engine. Make sure the SRS light comes on for a few seconds and then goes back off. Turn the steering wheel lock to lock a couple of times. Make sure the turn signals cancel, the horn works, and the SRS light does not flicker. You're done!

Jeremy