I have titled the subject line to aid others in the “search mode”. After reading several dozen threads about not being able to get the trunk open. Aside from failures of the vacuum, and using the right key/sequence/pins and cam there is another type of failure the plastic cog on the outboard cam. The plastic cog operates the main latch – pushing it forward causing the top of the latch to move away from the trunk lid catch. Unlike the other cog that is metal this guy wears out or in my case just broke – the material looks like bakelite plastic. Myths that I found on the 300SD 126 - there is no magic pull cable under or behind the back seat. Removing the license plate light on driver side will only give you access to the vacuum lock rod which moves the plastic cog, and if the cogs broken you have accomplished nothing. Removing the license plate light on the passenger side gives you access to nothing. The entire lock assembly is inside the trunk body cavity encased in a brass (colored) like box assembly. I spent several hours looking this assembly over after drilling the lock out to see if there was anything else I could have done. Unless someone chimes in with something I overlooked this is the only way to get in when this part fails.
I guess it should be shared. When the lock was drilled out I used an 8” screwdriver at the 2 o’clock position at a 45-degree angle and struck it with a mallet, it popped right open. Replacing the lock mechanism is fairly straightforward. You will need to have the trunk latch held in the open position to install new lock. (I used screwdriver and bungee cord) Have fun putting the snap ring on the cam – very tight quarters.

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My 300 sd 1985 MB trunk will not open. the vacuum works I can hear it when I lock and unlock the drivers door. and when I push on the trunk latch button it goes click, and the trunk opens a bit. but that is all. about 1/4 to 1/2 inch at max open and it will not open any further.

I purchased the 85 like this 10 day ago. so I have no idea what the innards look like. If I did I might be able to use a jimmy to get to the release.
could you or any reader send me a picture of the latch so I can at least try to pry the latch open? I'd rather do all that stuff than try to cut holes. I have no idea where the spare is or anything in the trunk as I've never had it open. thanks in advance for the help.
thom