You are on the right track with all of the components you are planning for your 2006 Buick Terraza but there is more information needed to determine what rise/drop ball mount you would need.
I attached an FAQ that details how to pick out the correct ball mount. Picking out the correct ball mount will allow your trailer to sit as level as possible. Basically you will first measure the height from the ground to the top of the receiver opening on the hitch while on level ground. Next, you... view full answer...
For your 2005 Buick Terraza if you are using Curt harness # 56077 the connection points on the vehicle are located behind the driver side tail light. I have included a link to the right to the installation instructions. I have also included a picture that shows the location. view full answer...