I wanted a solution to adding motors that is non invasive, does not destroy any "prime" parts, and simple to use. This is what I came up with.
You will need for each interface:
1 2x2 tall Lego brick, any color
1 2 position screw terminal block
about 2" solid core wire, 22-24 AWG
Small drill bit or finishing nail
Diagonal cutting pliers, smaller is better
Fine tip sharpie
Step 1: Mark and Drill holes
Step 2: Add conductors and solder
Strip 1" of wire for each stud/terminal. Bend an 1/8" down and insert through the hole in the stud. Insert the terminal strip on the side of the brick and tape in place. I found it easiest to put the wire in the hole, and then attach a power bus brick on the top, so I can test to make sure it makes connection. Solder the wire to the screw terminal contact and repeat for both studs. Make sure the wire points out at a 45 degree angle to the outside to ensure it makes contact with the electric bricks. Careful not to muck up the inside of the brick with the hot iron, if you do, just clean out the excess with the exacto knife.