If you mean it won't close at all, then not sure. If you mean it needs to be slammed and not just "normally" shut to catch the locking mechanism then try removing the two bumpers that are on the trunk lid.
I did that and it helped a lot. I kept on not shutting it all the way and the trunk light kept on staying on and since I normally don't drive every day a couple days would pass and that light would kill the battery.
Removing those bumpers and also making the light operate by a manual switch also helped in case I still don't slam it fully. I will get groceries and then see the trunk light open indicator as I go home sometimes
but luckily the trunk when closed down but not locked won't pop open at all when driving.
Trunk light switch:
http://www.ft86club.com/forums/showp...ostcount=20130