My trunk want open,the license plate lights are off an the 3rd break light is out an its not the battery

Remove the wheels if possible.
Remove the two clips from each side (by pulling up the center).
Move the fender liner away to access and remove the 7 mm bolt that is near the corner.
Unscrew the four cargo anchors from the floor of the trunk.
Move the trim panel and remove the 4 10mm bolts.

To get to the license plate lights assembly, you can follow these steps:

Open the rear compartment lid and locate the license plate light assembly inside the trunk lid.
Above the license plate, locate four Philips head screws holding the license plate light assembly inside the trunk lid.
Remove the screws (caution: in winter, plastic is extremely fragile and can break easily).
Once the screws are off, your license light assembly is loose inside the trunk lid.

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You should have a trunk lock cylinder in the trunk lid. Look to the right side of the license l plate by the license plate light and you will see a black plastic cover. Remove the cover to expose the lock cylinder then use your key.

I had the wires broken inside the loom that comes up from the trunk to the trunk lid. The wires bend by the right hand trunk hinge and break inside the insulation after years of opening and closing. I'm suprised that is the only ting in the trunk lid that doesn't work because the license plate lights, trunk release and the other running light wires also come through that loom and usually break.

check behind back seat for a release

Actually if you look right above your license plate there is a plastic cover covering a key hole on your trunk. Look right up buy license plate lights remove the plastic cover and you can manually use a key to open the trunk.

It's a black cover right next to the switch you press to open the trunk. I have an S80 trust me it's there nobody knows about it.

CLS550 2010. Same complaint trunk won't open, third brake light and license plate lights not working. Two ground wires (Brown) were broken inside the bundle of wires right were the zip tie holds them to the trunk lid arm. When I first looked I missed them. Remove all the corrugated wire protection and look the wires over very closely. One of them was broken inside but the wire just looked kinked on the outside. The other was broken in too. 7/9/17

YOU HAVE TO OPEN THE TRUNK LID REMOVE THE BLACK PLASTIC COVER FOR THE TRUNK LID LATCH.REMOVE THE LICENSE PLATE LIGHT HOUSING FROM THE TRUNK LID.REMOVE THE BULB SOCKET FROM THE LICENSE PLATE LIGHT HOUSING.TO REMOVE BULB FROM THE SOCKET SIMPLY PULL IT STRAIGHT OUT OF THE SOCKET.

check your ground side of the light circuit

this is straight out of the book ok

1. Open the rear compartment lid.
2. Remove the rear compartment lid trim.
3. Pull back on the rear compartment trim panel.
4. Unplug the lamp connector from the rear compartment lid wiring harness.
5. Press the grommet out of the rear compartment lid.
6. Remove the nuts retaining the lamp assembly to the rear compartment lid.
7. Remove the bulb.

open trunk,

remove felt liner from rear of trunk, (liner directly behind rear lights in side trunk) should be 4 plastic Phillips head screws. Loosing screws, then slowly peel liner away. You will see 3 nuts on each side, removing these nuts will loosing the rear light lenses, so you can pull the lense away from the body from the out side to gain access to the license plate bulbs. Re-install in reverse order. While in there I would recommend replacing your brake light and reverse light bulb. Hey your already in there might as well do a little preventive maintance.