trunk lock

[pat q]

Since I bought my 86' 560Sl last year, I had a problem with the trunk lock. I could not open or close it using the master key. I was able to lock or unlock it using the central locking system locking the doors which would olso lock or unlock the trunk. I replaced the trunk lock but, the new lock (with a new key) did not do the job. I still can't lock or unlock the trunk using the the key on the trunk lock. What am I doing wrong??Where is the problem??
Thanks for the expert help,
Pat in New Jersey