Trunk Lock Issue

I had this problem on my 84 500SEL when I got it. I think the 84 380SE will be the same.It seems that the trunk is locked electrically by the alarm system if it has one. There should be a cable inside the car close to the left rear door (I say Should be because I never found one in my car) that you pull and have someone else push the botton on the trunk and it will open. Also try unlocking the doors with the key. Try both front doors as both have the switch in them to unlock the trunk. On my car, vacumn has nothing to do with the trunk lock. Hope this helps.

Paul McKechnie

MBs come with two keys, a Master Key and a Valet Key. You might be trying to open the manually locked trunk with a Valet Key, after it's been locked with the Master Key.

If you share the car with another driver, maybe you each are using different types of keys. If the other driver (with the Master Key) manually locked the trunk, and you are using the Valet Key for regular use, then your Valet Key won't open the manually locked trunk. Only the Master Key will.

The Valet Key will unlock the doors, fuel flap and start the car, but won't give access to a manually locked glove compartment or manually locked trunk.

The Valet Key will turn in the lock when trying open the trunk, but won't open it. It has to be manually unlocked with the Master Key.

Just to make sure there isn't some confusion about using the wrong type of key, I'd suggest finding the Master Key and see if that will manually unlock the trunk.

Heh heh... This is because of your alarm system... factory alarm system. What you have to do is make sure the factory alarm is still hooked up... located underneath the front passenger floor... plastic floor and there is a small device...

Then lock the car as usual with your master key on driver door... maybe the passenger door will do also... use that square handle one... lock it and then unlock it... and see if your trunk can be opened.

If yes, then immediately disconnect the alarm unit... they do go haywired...

Make sure you keyhole for the trunk lock is vertical position.

Ah-ha! Thanks Tiger, I'm going to check it out on my 84 300SD.

I have the same sort of problem. My solution was to wail on the lock button with my thumb until it (the trunk lock) surrendered. Once unlocked, it works fine. It needs a reminder once in awhile (but my thumb has time to heal in between training sessions!).

Tim Delaney