I have a E320 1999 the rear head rests will not fall when I push the button on the dash. any ideas? Is there a release somewhere to lower them? Thank you. also I am not sure if this is air controlled. I think the trunk air mech was disconnected. the latch was replaced on the trunk. now it only opens with a key. not sure if that is related. thanks

The switch on the dash is electric,which somehow is translated into a vacuum
release of the headrest locking(upright) mechanism.
Whoever "Fiddled" with your trunk vacuum operation may have "86ed" the
headrest vacuum operation.
If you'll look up under the "Hat shelf" [where your rear speakers are] from
inside the trunk; you'll see how that end of the system operates.

thanks, is there a way to lower the headrests without the vacume or the switch?

Two ways I can see.
1.Pull the vertical covering in the front-most portion of the Boot(Trunk)
'looks like grey felt,it's fairly stiff so do not just jerk it out.Look up
You'll see a white hard plastic vacuum line with a blue stripe going
from each headrest actuator (looks like a thick black hockey puck)
over to a pass through grommet on the driver's side.'Just before
the grommet is one of the "F" shaped rubber vacuum connectors.
Apply a vacuum to the single port on the rubber connector(after
you pull the hard plastic line out). EASIEST
2. Remove the rear seat backrest(after removing the seat cushion)
find the white hard plastic,with a blue stripe vacuum line passing
through the rubber grommet on the driver's side from the lower trunk.
Pull it loose from whatever black rubber connector it feeds into in
the passenger compartment and apply vacuum. LESS EASY

OR, buy a MityVac (Vacuum/Pressure Tester) [Auto Zone,Harbor Freight]
and diagnose + fix whatever the P.O.'s wrench turner botched up.

thank you I will try that.

I have a '86 300E so I am not sure if this helps, my rear headrests would not fall with the switch. The source of the issue was a disconnected vacuum line going into a rubber connector near the fusebox (under the hood, driver side). I was cleaning out some debris in the area and must have dislodged the connection. All I had to do was push the line back into the junction.

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'86 300E 5 speed
'71 Triumph TR6
'46 Cushman Scooter
'41 Ford 9N tractor