I purchased the Hagstrom KE-72T for my interface device. This is a slick piece of equipment. It was easy to understand and it worked perfectly the first time. I wired up the grounds first and basically daisy chained them ALL to 1 ground terminal on the block. I went solderless all the way. I purchased some quick disconnects and used those everywhere. It was VERY easy and seemed to work well. When I would finish a series of buttons I would check continuity with a multimeter. This helped because I had screwed up a couple of my crimps.

The KE-72T has a port for my trackball and another for the mouse buttons. If you look at the photo of my CP, you will see 2 black buttons above the spinner. These are the left and right mouse buttons.

You will see from the photos that all the switches go into 1 terminal block. I have the option of adding another block if needed.