Latest: The new part arrived today. Everything fits. I've taken a photo of the old one and the new one side-by-side so you can see the damage to the old one that prevented it from working properly. The ears are just gone, with pieces up inside the back of the electrical switch.
Had a spot of bother getting that buzzer switch off the old one, but got it by working the new one until I saw that the steering lock plunger had to be in the correct location for that to come out. So I did that and then pried up the back (end away from the contacts) and applied gentle pressure to the front. Pop! It slipped out. Tested okay with a Multimeter, so installed on the new housing. Ready to go back in when I get some time between giving exams this week.
More to follow...

John Bonds, 82 240D, daily driver (when operating).
Mount Pleasant SC

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News from the front: Switch housing back in the dashboard and hooked up. The key and lock turn the switch when inserted without the black collar, but when the collar is put on, the key won't move, nor will the key come out. Take the collar off and the key can be removed. Done it four times now.

I think that when I turn the collar, the lock cylinder is rotating and the lugs are coming out of the lock cylinder housing. In the middle of the night I remembered that someone here advocated cutting the edges off the valet key so the cylinder could be kept deep iinside the housing and fully seated while the rotating collar is put in. I'll try that this morning.

jb

Done. I did the valet key shave (but in retrospect, not sure it was required). It did allow me to push the cylinder right into the socket and hold it there while screwing the cap into place. But when I did it, and removed the paperclip, the key wouldn't turn. So, following a comment I had read here, I pushed the paperclip back in and unscrewed the black cap until the lines on the cap lined up properly (in position 1, where the key must be for the lock cylinder to go in). Then pulled the clip out, and it worked fine. I think that it is necessary to line up the cap and the key, as otherwise, the plunger on the top of the cylinder can't come out into that channel in the cap. Without that in place, the key won't turn. So, try lining up the cap properly before sawing up your valet key!

Putting the lower panel back into place was hard, too, of course. But perseverance and colorful language prevailed after a couple of hours struggle. And I had the vacuum and electrical stuff right, too. So it started and shut down flawlessly.

Hooray. Got a daily driver again.

One more hint for unscrewing the black cap after depressing the paperclip and cam on the lock cylinder. If you can't get enough torque with your fingers, try the flat blade of a screwdriver as a pry from the right lower quadrant of the thing, prying it CCW as you try to turn with your left hand. Worked for me during those five tries.

Finally, having become more intimate with this ignition lock assembly than I would like, I must say that it is really an elegant device--typical of M/B engineering. Like a lot of other things on these cars, it was designed for a life-cycle of 25 years, and served flawlessly for 28 years. But it also illustrates what we must expect beyond that period of reliability. In the last 2 years, I've replaced the original clutch (it was really the throw-out bearing, but did it all while it was apart), most of the moving suspension parts, vacuum pump, had the sunroof mechanism overhauled, replaced the front wheel bearings, two starters (I think that the core problem with both was low voltage to the solenoid from that defective switch) and a window pane (the metal frame at the bottom rusted apart and jammed). The cruise control stopped working five years ago, I'm still chasing some vacuum leaks, and the fuel tank is still clogging my primary filter after three tanks of fuel despite Staron treatment. So there is still (and continuing) upkeep required. But they are great, solid, classic cars and deserve long life.

John Bonds, '82 240D 4sp, daily driver (again), 200k
Mount Pleasant SC

Having driven the car now for several days, it starts better now than I remember. The solenoid engages immediately and the starter works vigorously. The engine starts almost instantly. Far better than I recall for years. Again, I think my long-standing and persistent starter problem was this wearing-out switch rotator. So I suggest you check that starter by jumping it (instructions are here in the forum), and if that works then investigate the switch! I shoulda done that several years ago.
John Bonds, '82 240D 4sp 202k, daily driver
Mount Pleasant SC

john, I just posted a thread that my car does nothing sometimes when I turn the key in the ignition switch. Sometimes it takes 3-4 tries b4 it takes.

Was this your symptom?

84 300D

__________________
the sooner you start... the sooner you'll get done If it ain't broke, don't fix it.. Its always simpler to tell the truth...
2007 Honda Accord EX
2007 Honda Accord SE V6
96 C220
97 Explorer - Found Another Home
2000 Honda Accord V6 - Found Another Home
85 300D - Found Another Home
84 300D - Found Another Home
80 300TD - Found Another Home
Previous cars:
96 Caravan
87 Camry
84 Cressida
82 Vanagon
80 Fiesta
78 Nova
Ford Cortina
Opel Kadet
68 Kombi
Contessa

I am R&R the ingition switch assembly in a 1985 300DT

In the Exploded drawings the Diesel911 provided, it shows a item (#8) in 2 drawings that is refered to as " Contact Switch ".

How does one release and remove the switch?

Thanks for the help.

HammerWerfer

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1985 300DT 241,000 miles
1979 300SD 202,000 miles

I disabled the column lock on my wife's TD. It started to jam up on her. The tumblers were new. I took the tumbler assembly back out and wedged some plastic down in the recess where the back of the tumbler engages the column lock. Problem solved. I had to remove the whole assembly like you did once before and I was not in the mood to do it again.

I think that is what you need.

Turn locking cylinder into position "1" and remove contact switch (8) from steering lock. (as per the FSM.)

Charlie

__________________
there were three HP ratings on the OM616...

1) Not much power
2) Even less power
3) Not nearly enough power!! 240D w/auto

Anyone that thinks a 240D is slow drives too fast.

80 240D Naturally Exasperated, 4-Spd 388k DD 150mph spedo 3:58 Diff

We are advised to NOT judge ALL Muslims by the actions of a few lunatics, but we are encouraged to judge ALL gun owners by the actions of a few lunatics. Funny how that works