What type of AIS do you have? Most older AIS's transmit infomation via
NMEA 0183, most probably at a baud rate of 38,400. The RS233 is just the
plug, which is typically using only two wires to transmit
NMEA formated data. Once you have worked out what format your AIS is transmitting and which wires you can cut the plug and / or create a splice to the wires and connect the wires to a suitable multiplexer. I had to do something similar to connect to my
Raymarine instruments as there were no spare plugs in the back of the controller. Created a splice in the existing wires to connect to the multiplexer.
Ilenart