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Old 08-14-2011, 12:01 AM
sixto's Avatar
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DIY 87 300D combination switch

Putting this out for review -


W124 (87 300D) Combination Switch

The combination switch includes the switchgear for the turn signals, windshield wipers and cruise control. The cruise control switchgear can be separated from the main combination switch but 95% of the work is common. Unlike in a W123, the W124 requires removal of the steering wheel and lower dash panel to remove and replace the combination switch. Let's get to it!

My tool list includes:
- Philips screwdriver
- Flat tip screwdriver
- T25(?) Torx driver (or 4mm wobble hex key)
- 8mm socket and driver
- 10mm hex bit and breaker bar (or impact wrench)
- 24mm socket (or long nose pliers)

Precautions:

- Since the airbag has to come off, disconnect the battery.
- Since the park brake release is attached to the lower dash panel, chock the wheels.

Removal of the steering wheel and lower dash panel are separate tasks. It doesn't matter which is done first.

Steering wheel:

There are two holes on the hidden side of the steering wheel, one on each side of the steering column. They provide blind access to screws holding the airbag to the steering wheel. I use a 4mm wobble hex key to loosen the screws. I believe the proper tool is a T25 Torx driver (which I don't have available to me). The screws are captive, meaning they remain attached to the steering wheel once the airbag comes free.




With the airbag free, use a small flat tip screwdriver to to pry the red connector from the airbag. I'm not able to pull off the connector with my fingers. Set aside the airbag.



Have an assistant hold the steering wheel while you remove the bolt holding the steering wheel to the steering column. The bolt takes a 10mm hex bit. Use as long a breaker bar as is available or try an impact wrench. It might be possible to use the steering shaft lock to hold the steering wheel but replacing the steering shaft lock is too involved a task, and I enjoy rebuilding engines and transmissions, for me to risk it. It seems like there is thread locking compound on the bolt. I wouldn't try heat because of all the plastic and wiring in the area.



With the bolt off, note the orientation of the steering wheel so you can install it in the same orientation. Make alignment marks if necessary. Wiggle the steering wheel off the steering column. All the wires in the steering wheel can remain in place. Set aside the steering wheel.



Lower dash panel:

Pull off the headlight switch knob. Don't be shy, give it a good tug. Remove the nut revealed by removing the headlight switch knob with a 24mm socket. Long nose pliers seem like a possible alternative.





Pull the left end of the outboard black trim panel away from the dash. There are two clips on the narrower portion of the trim panel that might need a little prying.



The trim panel will be retained by the headlight switch illumination bulb. Squeeze the sides of the bulb holder and wiggle it off the trim panel. You might have to squeeze the top and bottom of the holder rather than the sides. The inside end of the trim panel tucks under the steering column trim so pull away from the dash and away from the steering column. Set aside the outboard black trim panel. Remove 3 screws using an 8mm socket and driver.




Pry the right end of the inboard black trim panel, the one around the key switch, away from the dash. There are 3 tabs to release while pulling away from the dash, then pull away from the steering column. Set aside the inboard black trim panel. Remove 2 screws using an 8mm socket and driver. Note that the screw closer to the key switch has a smaller washer.






Remove 2 black screws under the park brake release handle using a Philips screwdriver.



Remove 1 screw holding the hood release lever to the dash.




Pull the hood release lever downwards and away from the dash. Note the hammer end of the hood release cable and rotate it such that the hammer and cable slide through the slot free of the red handle. Slip the cable out of the black guide tube. It might be possible to leave the hood release lever attached to the lower dash panel but I find insufficient room to work on the various electrical connectors.




The park brake release cable can remain attached.

Remove 2 screws along the bottom edge of the lower dash panel using an 8mm socket and driver.



Pull down the lower dash panel. Note that the lower dash panel is somewhat pinched by the steering column trim. You should have enough room for the work to be done without completely removing the lower dash panel.




Combination switch:

Locate the 14-pin connector below the silver cruise control unit outboard of the steering column. Separate the 14-pin connector. The female half of the connector has a retention tab molded into the case but I don't see where it can attach.



Locate the 6-pin connector outboard of the silver cruise control unit. Separate the 6-pin connector. The female half of the connector is fixed in place.



If you plan to fully remove the airbag contact plate, locate the red 2-pin connector. There is a tab in one end of the connecting halves. Either push in the tab or pry up the corresponding slot to separate the halves.



Locate the wire tie holding the wire bundles from the 14-pin connector and 6-pin connector. Push the tab in the wire tie away from the slotted surface of the wire tie and feed the loose end of the tie through the retainer to enlarge the opening of the wire tie. No need to fully open the wire tie.





More to come...

Sixto
87 300D


Last edited by sixto; 08-14-2011 at 12:12 AM.
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  #2  
Old 08-14-2011, 12:01 AM
sixto's Avatar
smoke gets in your eyes
 
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Remove 3 Philips head screws holding the airbag contact plate to the combination switch. Set aside the screws.



Pry the airbag contact plate from the combination switch. You can leave the contact plate dangling. The blue sheath around the airbag wires can be brittle and fall apart as you move the airbag contact plate. If you want to remove the airbag contact plate, thread the blue sheathed wire bundle from the released red 2-pin connector through the enlarged wire tie and up the steering column trim. Set aside the airbag contact plate.




Remove 3 Philips head screws holding the combination switch to the steering column. Set aside the screws. Note that a longer screw without a washer(?) holds the cruise control switchgear to the combination switch and steering column.



Pry the combination switch from the steering column. Thread the wire bundles from the released ends of the 14-pin and 6-pin connectors through the enlarged wire tie and up the steering column. It is a tight fit for the 14-pin connector around the telescoping steering column switch (if equipped) in the steering column trim. Set aside the combination switch.





Although the telescoping steering column switch and motor are visible at this point, there is considerable disassembly of the steering column required to remove the telescoping steering column motor. The switch is easy to replace at this point but it looks to be part of the steering column trim. With the combination switch out of the way, the steering column switch pulls easily off with the steering column.




Haynes time! Assembly is the reverse of removal. For the most part, it is.

Some things to look out for:

- There is a piece of rubber trim around the cruise control stalk. The edges of the trim are slotted to go around a tab in the steering column trim. Get this piece of rubber trim correctly in place before the steering wheels goes back in place.




- Neither my car nor the two combination switch donors had a piece of rubber trim around the turn signal stalk.

- Route the wire bundles through the wire tie and retighten after all the wire bundles are connected.

- Do a trial fit of the lower dash panel to ensure all the insulating pads and wires are clear of the screw holes.

- Make sure you thread the hood release cable to the slot in the lower dash panel through which the cable reaches the hood release lever. You can wait until the lower dash panel is securely in place before attaching the hood release handle.

- Set the hood release cable back in the black guide tube set the hammer and cable in the hood release lever.

- Make sure the nut clips for the screws holding the lower dash panel in place are in place and did not slide out of place or fall off.

- Don't forget to attach the headlight switch illumination bulb and holder to the outboard black trim panel.

- Note that there are 2 pins in the airbag connector. I don’t believe there is clocking or polarity to consider.



- The airbag retention screws are self aligning and pretty good at it too. Turn the screws while holding the airbag to the steering wheel and the screws should engage and tighten.

Moment of reckoning:

- Decide whether you can live with any leftover parts

- Reconnect the battery and make sure everything works as it should. The airbag warning light shouldn't remain illuminated after the engine starts.

Sixto
87 300D

Last edited by sixto; 08-14-2011 at 12:15 AM.
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  #3  
Old 08-14-2011, 12:16 AM
sjh sjh is offline
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SWEET!!!

Nice job.

Why doesn't my w124 have an adjustable steering wheel or headlights?

.
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  #4  
Old 08-14-2011, 12:20 AM
Aquaticedge's Avatar
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Awesome Write up. I considered doing this Job when my cruise switch was busticated. Kinda glad I diddnt! Very involved process but a nice write up
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  #5  
Old 08-14-2011, 12:24 AM
sixto's Avatar
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Quote:
Originally Posted by sjh View Post
Why doesn't my w124 have an adjustable steering wheel or headlights?
Part of a package including leather seats and memory driver seat.

Another package is heated seats and ASD (leather not required).

The ultimate option is orthopedic front seats. I don't know if leather is required.

Sixto
87 300D
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  #6  
Old 08-14-2011, 12:27 AM
sjh sjh is offline
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Any chance an adjustable steering wheel could be (practically) retro-fitted?

With your write-up. I suggest folks make sure they have grounded themselves, no static discharge, before they touch the air bag contacts.

Great write up. It must have taken you half-a-dozen hours.

Nice gift to the site.

Are you going to the Oakland BBQ?

.
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  #7  
Old 08-14-2011, 12:31 AM
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Well done. Always nice to see lots of pictures. I did this job last year. Not a bad job but long, kinda like pulling the dash. The red plug should engage the airbag socket with a clearly audible "snap" according to FSM (mine did). Make sure the key is in your pocket and the battery disconnected before playing with the airbag, "just in case."

SJH, I thought the adjustable steering wheel was standard in all US-bound 124s. My car has the adjustable steering wheel, memory seat, etc., with MB-Tex seats but without heated or orthopedic seats. The adjustable headlights were a Euro-only option, DOT never approved them (or Mercedes didn't ask) but they can be retrofitted -- I am doing that installation now, as it turns out.

It may be possible to remove a complete adjustable steering column from a donor car and transplant it to yours; the steering wheel position is stored in the seat position memory, BTW. If you don't have a driver's seat memory some wiring changes would be necessary.

Jeremy
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Old 08-14-2011, 12:50 AM
sjh sjh is offline
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Quote:
Originally Posted by Jeremy5848 View Post
SJH, I thought the adjustable steering wheel was standard in all US-bound 124s. My car has the adjustable steering wheel, memory seat, etc., with MB-Tex seats but without heated or orthopedic seats. The adjustable headlights were a Euro-only option, DOT never approved them (or Mercedes didn't ask) but they can be retrofitted -- I am doing that installation now, as it turns out.

It may be possible to remove a complete adjustable steering column from a donor car and transplant it to yours; the steering wheel position is stored in the seat position memory, BTW. If you don't have a driver's seat memory some wiring changes would be necessary.

Jeremy
Jeremy,

My '90 OM602.962 has no-memory seat (which is OK with me). All I'd really like would be the steering wheel adjust, more in-and-out than up-and-down. Memory doesn't matter. Headlights don't matter. Heated seats, leather, orthodontist doesn't matter.

But my body proportions, short legs - long trunk doesn't fit the existing envelope as well as I'd like.

Do you think it's practical and feasible to do this or am I just dreamin'?

.
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Old 08-14-2011, 01:19 AM
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The pictures I've seen in FSM show the adjusting motor to be built into the steering column. That suggests that you could remove one from a donor car as a single unit, ready for transplant. To be safe, I would take everything below the steering wheel and down to where it attaches to the steering box, possibly including even the steering lock.

Interesting: "An electrically adjustable telescopic steering column is standard equipment." (1986 W124 "Introduction into service" manual, page 208) Note that adjustment is "in and out," not "up and down." Range of adjustment is 60 mm (~2-1/3 inches).

Jeremy
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"Buster" in the '95

Our all-biodiesel family
1995 E300D (W124) . .239,000 miles My car
1996 E300D (W210) . .313,000 miles Wife's car
Santa Rosa population 170,685 (2012)
Total. . . . . . . . . . . . 722,685
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970
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Old 08-14-2011, 01:34 AM
sixto's Avatar
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MB didn't figure out tilt steering until the W140.

The FSM (section 46-7700) makes it seem straightforward. Beyond the steps in this DIY, release a couple of nuts and bolts holding the column under the gauges, another couple of nuts and bolts at the firewall, and a nut and bolt at the steering box coupling. Removing the steering lock (section 46-8010) is the most complex step because of a number of mechanical, electrical and pneumatic (vacuum) connections. Not to mention the funky way MB key cylinders are removed. And you're working in tight quarters.

Jeremy brought up a good point about the steering lock. I don't know if they're different from year-to-year and between gas and Diesel.

Sixto
87 300D
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  #11  
Old 08-14-2011, 02:03 AM
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Quote:
Originally Posted by sixto View Post
The ultimate option is orthopedic front seats. I don't know if leather is required.
Mine has Palomino texmex and ortho seats, so leather is apparently not required

A couple questions:
1. What are the dual plunger switches in your doorframe for?
2. What does the economy gauge on your instrument panel read, since you have no manifold vacuum?
3. What's the story with the AFTERGLOW light?
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Old 08-14-2011, 02:25 AM
sjh sjh is offline
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Quote:
Originally Posted by Jeremy5848 View Post
The pictures I've seen in FSM show the adjusting motor to be built into the steering column. That suggests that you could remove one from a donor car as a single unit, ready for transplant. To be safe, I would take everything below the steering wheel and down to where it attaches to the steering box, possibly including even the steering lock.

Interesting: "An electrically adjustable telescopic steering column is standard equipment." (1986 W124 "Introduction into service" manual, page 208) Note that adjustment is "in and out," not "up and down." Range of adjustment is 60 mm (~2-1/3 inches).

Jeremy
Well I'm lucky it moves in the direction I want.

Looks like I might have a project to add to my list.

Thanks.

.
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Old 08-14-2011, 09:37 AM
sixto's Avatar
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Quote:
Originally Posted by okto View Post
A couple questions:
1. What are the dual plunger switches in your doorframe for?
2. What does the economy gauge on your instrument panel read, since you have no manifold vacuum?
3. What's the story with the AFTERGLOW light?
1) One is for the cabin light, the other is for the alarm. Maybe they use a single switch in your 95.

2) I use it as a boost gauge. I reset the indicator on the bourdon tube device such that it indicates 5-12 psi between posts. Jeremy uses it as an engine vacuum pump monitor. You drive a 603 with one eye on the temp gauge so you might as well have a boost gauge where you'll see it

87 300D gauge cluster innards and boost gauge mod

3) I installed an afterglow relay and coolant temp sensor for full afterglow function. I hooked up the blank warning light space to the #1 glow plug so I know when it's glowing. The yellow glow indicator goes out long before the glow plugs go out.

Sixto
87 300D
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  #14  
Old 08-14-2011, 09:59 AM
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Quote:
Originally Posted by sixto View Post
Part of a package including leather seats and memory driver seat.

Another package is heated seats and ASD (leather not required).

The ultimate option is orthopedic front seats. I don't know if leather is required.

Sixto
87 300D

I have memory drivers seat, and power steering wheel, but MB Tex. I have a friend with MB Tex Ortho seats in his 250D.

My 1991 SDL has ASD, and leather but no heated seats, sort of disappointed, it has every other option, girlfriend is pissed about the lack of heated seats lol.
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Old 08-14-2011, 10:48 AM
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nice write up! I'll submit it to consideration for the wikki!
thanks for the work!

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