Step 7: Connect GPS Unit
We will actually start connecting devices at this point. As noted earlier, the green wire (from RX pin connection on GPS unit) will go to the TX pin (digital 0) on the Uno. The power cable will go to Digital 8. The ground will stay out for now. We'll later attach the ground lines from other peripherals to this wire as many things need to share a common ground.
One thing to note about the GPS unit with this connection: The RX/TX connection pins replaces the serial communication of the USB serial cable once this unit is powered up and running. Thus, if the GPS unit were cabled up to the 3.3V or 5V connection vs. the digital pin you would not be able to upload code to the Uno as the GPS unit would be using the Serial. One should use a similar wiring approach when testing the GPS unit to allow for code uploading. Otherwise you will need to disconnect either the power or serial wire each time you need to upload code.