If as I suspect the 3300c uses the LGC2000 gps unit, it is in fact a mini NMEA2000 network between the GPS & the display, in which case you will need to power both the NEMA2000 Bus and the display as follows:-
"to power an NMEA 2000 buss, you will attach both the
NMEA 2000 Power cable and the unit's Power Supply cable to the
boat's battery. To attach the NMEA 2000 Power cable, connect the
red wire to battery's + and black and shield wires to battery's –." here is link to the manual that explains it all.