RTFI? It is in the instruction manual and if you don't have that you can download one from Navman's website. The connections are from memory in the power lead and you may need to disconnect the boat end of this if the NMEA leads have been cut off flush, re-strip the outer cable and you will find the NMEA leads, then remake the power connections to the boat and connect NMEA to the DSC.
I did this job on my boat a couple of years back. I couldnt find the correct wiring info and had to get instruction from Navman on the phone. Did not need another lead but the sequence of which wire to connect to which was not obvious. I think the Navman products are great but why if you buy their plotter and radio you have to mess around making connections when they could supply a pre done lead is a mystery.
The navman will have a minijack socket for an external speaker which is a round plug. The 5500 plotter has a power and data cable for connecting a GPS aerial (round multi-pin connector) and for connecting data and power. The NMEA is sent via the white = nmea out and the black which is nmea earth.
I have both the 5500i and the 7200 and you get the plugs at both ends but you have to connect them yourself (marine connector block - like you get at B&Q but 10 x as expensive as it is stainless steel) the follow the instructions for setting the right parameters on the plotter. All very simple