Assembly Assistance for the Printrbot Simple - 3D Printing: Build your Own 3D Printer and Print your own 3D Objects - page 60

Figure 3.22 A closeup of the Simple circuit board.
I'm hesitant to point out any particular ports on the circuit board because these
could easily change in future versions, but one thing I do wish to point out is that
every port is labeled. This makes it easy to match up the motors and hot-end to
their proper ports. For example, in Figure 3.22 , if you look at the very bottom of
the board, you'll see a white port with the letters T-EXT. The hot-end is constantly
sending its current temperature to the circuit board (and on to the software used
in 3D printing), and you'll need to make sure to connect the proper wire coming
from the hot-end to this port.