Mike,
They need to be connected via NMEA0183. The power wire from graph should have a brown, blue pair of wires for NMEA0183.
Since the smartcraft gauge is RX only (receive – no transmit TX), connect the blue wire to pin 8 on the smart craft. The gauge should have a few tag end wires coming out of the back. The orange wire will be pin 8. If the wires are no there, it would be the top left pin (verify that with smart craft manual).