Hey all. I got a '79 SD that was hit in the side by a Durango. It was hit on the drivers side rear, has a dent but everything worked except the back door. I got it before being salvaged and have a restored title on it.

The trunk worked fine when I got it. When I unlock the door the broken door even unlocks. Same with fuel tank and everything else. Recently I cant get the trunk open. I can push the trunk pop in and out, but no pressure and the trunk does not open. I tried with my keys too, and can turn it quite a bit but the trunk pop never pops the trunk.

Because the key does not work and all other vacuum operated devices work, and the fact that the key turns but the trunk wont pop, leads be to believe there is something else that wont let it open. Ive probably read most of the posts on this form about this same issue, and tried the ideas. So does anyone have any other suggestions on what could be done? And if not, is there a way I can get it open and rig it so the trunk will close but not lock? I dont have any worries about anyone stealing my cubes of veggie oil out of the trunk.

Thanks!

The lock cylinder key slot should be vertical in order for the vacuum system to lock/unlock the latch. Inserting the key vertically and turning it counterclock wise while gently pushing in on the release knob should release it. If you insert the key vertically and turn it clockwise so the slot is horizontal and remove the key, it should remain in the unlocked mode. Unaffected by locking the doors with the key. This is assuming it works as designed.

Assumptions:
You are using the proper ket NOT the round head key
You are turning the key CCW and pressing in the lock
This lock recently worked
You are not using a brass key

Plan A:Try operating the key while applying vacuum to the line under the pass. floor mat / black plastic covering.
Plan B: The above with two roughly 1" x 1" x 12" pieces of wood flanking the key while in the lock and CCW, smack the sticks with a hammer.
Plan C: Call the MB hotline and ask for advice

Ok update:

I tried every possible way and found that the vacuum is working, the trunk popper is just not catching on for some reason.

I unlocked the car, tried unlocking the key from going vertical, to horizontal, and then past that to 8:00 position. When in this position I can push the button in and out but nothing popps and there is no "pressure" needed to push the button in.

When I LOCK the driver door to activate the pump, it is in horizontal position. If I try to move the key vertical, it tries to go back horizontal - so that tells me the vacuum is good.

So at this point it just does not seem to catch. Is there something I can do about this or do I have to break into the car somehow by drilling or cutting holes? I dont want to but I do really need to get into this trunk. My dead bodies I have in there are starting to smell

I need to post a correction to my above post. I just got back from lunch and tried the trunk lock. The key slot is horizontal (not Vertical) in the central locking postion. i.e. the trunk can be manually opened once doors are unlocked from drivers door. If the central locking is engaged, insert the key into the horizontal slot, turn to the 7 o'clock position, then push in on the button with the key in the slot. Try some lube, WD40 etc in the slot. You say you turned the key to the 8 o'clock position, then pushed the button. Maybe you didn't go far enough? Mine is a little reluctant to turn counterclockwise probably from lack of use or slight wear on the key? Until today, I cannt tell you the last time I used the key to access the trunk.

Ya I understood what your talking about. I know how to open with the key, and can not open it with the same key I used to be able to open it with. It is not a valet key. The problem is everything turns and such, but the push button does not have any resistance. No matter what is done with the key, it freely pushes in and out. The vacuum seems to work. So there is something else that is not allowing me to pop the trunk.

I have read that there are some cars that have alarm systems and an electronic system that is also needed to unlock the trunk. I think this car may have it because when I had a dead battery in the past, I had the same problems I am having now - and once I had a good battery I was able to open the trunk fine.

Any help would be greatly appreciated.

If all else fails, Break out right rear tail lens. First find complete replacement from boneyard. Dont pay more than $30. Place a small section of 2 by 4 over the lens. and hit with rubber mallet. Then loosen the bolts that mount the trunk lid. get the ones on the left through the medical kit. then remove the bolts atttaching the latch from inside. then wiggle the trunk lid foreward.This should give it enough play to come open. Before doing all this I would search this website for trunk latch problems and try all other options. Its a last ditch effort. I had to do this when I got a wingnut stuck in my latch. not fun breaking a nice taillens, but it took a fraction of the time i spent trying conventional methods. Also try going to the boneyard and studying one that is simular to yours. then you will figure it out easily.

Ok searching further, I found several people with similar issues but no resolution. I have the small black box in the passengers side foot area... for the alarm. No alarm is set up, but that box is there with a connector. From what I am reading that not activating will cause exactly what is happening. So how would I bypass that alarm system? Is there wires I can apply 12 V on to activate and unlock the trunk?

Also as far as getting the trunk open, is there anything else besides breaking out tail lens? I dont have any junkyards around, and my lens is dented from the accident it was in... so even if I got a replacement, it would be very difficult to install.

Can I cut a hole under the trunk or under the licence plate? Or what about drilling out the lock? Would that help at all or just cause un needed damage? I dont care about locking the trunk, just want trunk access

bump

bump again. Anyone know anything about the factory alarm and how to disable its keeping me out of the trunk?

Somebody tell me if I'm wrong, but I dont remember a "factory' alarm in 1979. I was an advisor with the local MB dealership from 88 till about 93 and dont remember any alarms on diesels of that era.

FACTORY alarms with the trunk electric actuator ( a specific redundancy for factory alarm only) was not used until some of the 1984 models; and even then, not all. My 1984 300SD has it; some friends' don't.

There are two wires that go to a plug to the actuator (mine's now disconnected ). On my car, the wires enter the trunk from behind the rear sea back area on the passenger side.

I find it hard to believe a 1979 would have this; but, who knows?

__________________
The Golden Rule

1984 300SD (bought new, sold it in 1988, bought it back 13 yrs. later)

I believe mine does. But of course im not positive. I checked, and I do have the vacuum lines that go to the trunk behind the passenger side rear seat, along with a lot of other wires.

Assuming it has the same system as the 84sd like mentioned in the previous post, is there two wires that I could short or apply 12 volts to, to unlock it? I also noticed a plug in my engine bay, passenger side next to the air cleaner assembly, that is not plugged in - its a 2 prong. But theres nothing around that i can plug the other end into. Could this have anything to do with it?

It seems that the vacuum is working ok, but still not able to pop the trunk. The button pushes in, but wont go into a resist mode so I can push it in and POP it.

If I cant get into it this way, could I try what others have done and drill with a 1/2" drill bit to get it open? I dont care if it locks, I just want to be able to open and close it. Thanks again!!!

If this car has an aftermarket alarm its function would be to sound off a siren or enable the cars horn to blow. It would not disable entry , it would sound off if the trunk was forced open. I read some recent posts about access thru the first aid tray opening. Remove the tray and use a long rod to trip the latch. I've never personally done this but the poster said it worked? Could you use a hand held vacuum pump and put vacuum to the hose that releases the latch? or just call a lock smith.

The vacuum works. The trunk open "button" just does not give resistance so it will pop. It is not a vacuum issue. If it was I would be able to open it with my key (standard key not valet) even if all vacuum quit working. I need a way to get the electronic auctuator to release the trunk, which would be controlled by a factory alarm.