Secondary Trunk Bolt Lock

I just ran into a situation with my trunk lock, on my 1989 560 SEC, that I thought would be a good idea to document.  Especially since the shop manual (on CD) doesn't really too detailed in the area of the trunk locking mechanism.  
I noticed that my trunk lid suddenly stopped conveniently popping open when I pushed in the trunk button.  I had to pull the trunk lid up while pressing the button really hard.  I thought maybe the striker simply need adjusting, but saw there really wasn't any adjustment.  In looking down into the latch mechanism (fig 2) everything appeared to be OK, no excessive wear and everything moved freely.  
The trunk locking mechanism is made up of two locks.  One, the primary trunk latch, this unlatches when the button is pressed and is locked by the central locking system or when the trunk key is turned straight up (12 o'clock).  The second is a secondary bolt mechanism, that's engaged when the trunk key is turned to the right (3 o'clock) and the key is removed.  When the trunk lock is in the 3 o'clock position the lock can not be unlocked with the valet key or with the central locking system. 

	Fig 1
	Fig 2

I removed the plastic cover over the rear trunk lip.  Plastic pegs (part of the cover) go through holes in the carpet and catch into holes in the trunk body.  Simply pop one out at time work from left to right.  Try lifting or pressing down while pulling out, to release the peg.  Once all the pegs have been released, the cover will hinge up and out.  The outer edge of the plastic cover has a lip that fits over the outer portion of the trunk body.  Remove the left and right taillight bulb holders and lay the carpet back to expose the truck latching mechanism.

Remember the only problem I was experiencing, was the trunk lid didn't pop open by itself.

Looking at the locking mechanism, I could see exactly what the problem was and was I glad I opened everything up (fig 3).  The plastic coupling for linkage to the secondary trunk bolt had popped off the ball joint connected to the lock lever and was in the way of the push button.  That linkage was not allowing me to push the button all the way in and not  fully retracting the primary latch (fig 4 & 5).

Fig 3
Fig 4	Fig 5

 The thing that had me concerned was, the bolt mechanism (fig 6) was free to slide into the engaged position with the linkage disconnected.  (and that bolt moved very easily)  If that bolt did engage, I wouldn't have known how to disengage it.  The trunk would be locked with no way to open it.  Now that I see what's happening in there, I would imagine if this ever happened, I could raise the left side of the car and jiggle the trunk lid while holding the button in.   In the hope I could walk the bolt back manually. 
When the trunk lid is open, there's a interlock paw that keeps the bolt from engaging.  Otherwise the bolt would keep the trunk from being closed.

Fig 6

The actual clip is a plastic joint (fig 7) that fits over a ball mounted at the end of a lever that is part of the lock mechanism and turns as the key is rotated to the extreme right.  To reinstall the joint over the ball, I inserted a flat bladed screwdriver into the slot between the round hole and square hole then twisted slightly to open the round hole a little to allow the joint to be pushed over the ball.  Since the lever the ball joint is connected to is made of white metal, I put something behind the ball to support the pressure I was applying to avoid breaking the lever.

	Fig 7

I'm not sure why the this linkage popped off, but if the trunk lid is open and someone forces the trunk key to the right (3 o'clock), it puts a lot of stress on that joint because the bolt interlock keeps the bolt from sliding closed.

Reassemble in reverse order.

Disclaimer
This procedure should be used as a reference and some applications may vary.  The author is not responsible for variances and this article may not be 100% accurate.  So proceed with caution and the reader accepts 100% responsibility for the results.

by Chet Hwilka