The larger of the lock "jaws", has a semi-circular tab that operates the trunk status switch. This is visible in the 1st picture. The reason these fail; turning on the trunk open light, message and chime upon driving, is that the minuscule pin gets caught in the much larger boot around it. This prevents it from rising and disconnecting from ground. The switch is melt riveted to the housing but the whole assembly is held with only two rivets which also serve as the shafts of the jaws. Freeing the pin can be done w/o removing switch from housing.
I purchased a new one, but the way this part is designed, it may fail again. Next time I know how to fix it. Access can be had by lowering the top.