I just bought a new Icom m412 radio and a shakespere 5225xt antenna. My problem is,I'm not getting the reading on the radio when I have one on my Humminbird 788ci. I called Humminbird checked to make sure it was compatible to the radio, it was so I ordered the linking cable. Parts arrived today, no wiring inst. Called again and was told what the 4 wires were,1 +,1 nmea out,1 grnd & 1nmea in. They said do not hook-up the+? Set the 788 to nmea on, no time, no location on the radio, any suggestions? Rudey