Not possible, as the full at-rest position of the cruise is merely idle on the linkage...it can't pull in reverse.

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my guess is the ignition key device is damaged, and the steering column through the lock mechanism when you push on the steering wheel, activates the vacuum portion of the device.
try just hitting the steering wheel and see if it shuts down.

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im in Virginia this state is real messed up when its come to inspections but like the one poster said my dummy self will problay hit the horn in traffic or something but i guess it be ok if i left the key on start postion but im going try fix it.. gonna take this thing cross country with a 9 year old this summer he is totally amped and i cant let the little guy down, thanks agian for all input ..this forum is freaking awesome and everyone on it

x2. bang on the steering column, dash, etc., and see if it shuts down.

I love the smell of diesel in the morning. It smells like.... diesel.

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mjk

'84 300SD 119KMi (Liesl der Diesel)
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Not a bad approach and worth a try. The fact that the horn also does not blow during the shutdown event was most interesting and still is.

The horn won't function if the key is turned off, so at least that aspect is normal.

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ok i went this morning started the car up like 5 times and when i tunred the key back the car cut off like it was suppose to each time...came in the house for 15 minutes then my dad came over we went out to start the car now its doing what it originally did when you turn the key back and hit the horn it cuts off ..also i was able to bang the crap out of the wheel dash etc to see if it would cut off before i hit the horn but it did not until i press the horn once

also a side note i rememeber a guy took the pin out of the steering column so the wheel would not lock

Try doing something else electrical like turning on the lights or wipers and see if that also shuts if off. Did you observe the linkages?

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Okay then I guess I also vote for the locking pin moving or something simular.Just giving a little boost or greater range to the movment arm for the vaccum valve on the electrical assembley.

There is possibly excess wear in the coupling to the vacuum portion of the electrical switch. . So the range of movement required for function is greater now than originaly designed.

If this is the case then it should be repaired before it becomes totally disfunctional. It will probably take some time to totally fail but could happen if it is indeed the wear issue it now looks like.

Simplified the connecting linkage on the electrical portion of the switch to the vacuum valve may have just worn out with too many activations over the years. Nothing lasts forever even if what you have is a very low failure rate item other than the electrical portion of that assembley is known to wear out.

Okay now the interesting part for you. Read all you can find in the archives about changing this part out. Go to an auto wreckers and if you can recover the parts needed yourself you will be confident of installing them in your car.

Before this though I would check carefully the vaccum lines to and from the vacuum control portion of the ignition switch. Making sure sure one is not pinched or kinked somewhere denying the vaccum feed to the shutoff valve on the injection pump. Unless pressing on the steering wheel frees up some form of restriction enough for the feeder lines to function..

This is what I was thinking as well. It's the only thing that makes sense unless the normal systems have been altered. What you need to do is pull the instrument cluster out and look down in at the ignition switch. If you have two vac lines running to a little vacuum valve that looks like the attached pic then your regular ignition system is intact. You can then pull the lines and test your shut off valve with a MityVac.

What I am not entirely sure of is what would enable this with the key turned back versus any other position. But it just sounds like somehow with the key in that position pushing on the column allow the valve to open enough to allow vacuum to the SOV.

Try this: see if you can rule out the actual horn portion of this by attempting the same thing by pressing on the column - just not directly on the horn. Or pull the fuse to the horn and try it that way as well. There should be no connection between the actual electrical current of the horn and the vacuum ignition, but at least you can rule it out in this manner and move on from there.

Attached Thumbnails

 

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"Back off, man. I’m a scientist” ~ Peter Venkman

the wipers nothing else will cut it off but the horn..i have also noticed then when the key is in forward postion the battery light is off and when i turn it slightly back or back it comes on , also when i hit horn the battery light gets brighter before it shuts off , i just turned the key very slightly back it didnt cut off wen i hit the horn just make that battery light glow stronger but when i cut it full back it glows real hard then shut off

Hmmmmm. So the problem could exist in the steering lock assembly. The root cause may be there and the pressure of pushing on the horm is allowing the ignition vacuum valve to open because the entire ignition steering assembly is now somehow out of alignment . . . idk, i'm reaching here. Nevertheless, if someone has altered the steering assembly, you need to investigate there, I think.

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'95 E300D ("Tank") - 231,000 miles
'79 240D ("Biscuit") - 197,250 miles (Sold)
'83 240D ("Ding-Ding") - 217,000 miles (Death by deer)
______________________________________

"Back off, man. I’m a scientist” ~ Peter Venkman

Is the engine trying to shut off before you hit the horn or is it idling along as if the key has not been turned. If the engine is stumbling, trying to shut off by vacuum, putting a load on the alternator might be enough to bring it to a stop. If it's idling as normal, this wouldn't be the case.
You need to look at the linkages and the shut off valve to see if any modification has occurred. I would even pull the vacuum line off the shut off valve so the ignition switch can have no effect on shutting down and try the sequence again--does turning the key off and hitting the horn stop the engine when the brown vacuum line going to the shut off valve on the back of the injection pump down between the injection pump and oil filter housing has been removed.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

no the engines runs in idle fine until i hit the horn...i also got my father to look at the linkage and nothing moves it just cuts off.. will try some of the suggestion and get back to you guys soon, i hope my buddy can come over soon he is much more mechanical than me..thanks agian