Elektric lock from the trunk lid does not unlock

[AdjeTovenaar1]

Hi all, from our Audi A6 C6 Sedan , 2008 the trunk lid doesn't work anymore. So if you open the lid manually, the elektric lock should open.
What I think, is that either the lock is defective of a fuse is defective. Or the microswitch, maybe. I can't find where this specific fuse is located. The lock is connected by 3 wires, a brown , a yellow-white and a green-grey. What voltage should I measure if the fuse is not blown? That could tell if i have to search for the fuse or not. how can i check what the problem is?

[Crasher]

Start with a code red of the central convenience system.