"Ben" wrote in message
om...
notation in the bottom-left corner of Z075InterfaceSch.jpg - can you
let me know what it says?

That is a sketch of the connector "from back" at 2 oclock "black", 4 oclock
"green" 8 oclock "blue" and 10 oclock "shield"

Second, do you know what IC2 in the ZO75 "does?" That is, does it
simply change the serial input to another sort of signal the autohelm
interprets, or does it sends signals such as "steer left", "steer
right" by activating the appropriate pin on the connector?

IC2 is the central 2K rom single chip computer and receives the NMEA 183
sentence on T1 (pin 39). The processor finds the Xtrac Error in the
sentence, determines if it is to port or starboard of the course and send
out a course correction on P23 (pin 24) or P24 (pin 35)..

it easy for me to use my laptop to write a program to interpret the
NMEA messages, and output "steer left" "steer right" commands on my
parallel port, and amplify them to the appropriate level before
inputting them into the autopilot.

If you receive the NMEA 183 on the Serial port of the laptop, process it
with your program and output it via a parallel port. Then just replicate the
relay circuit of the interface to control the AP remote connector..

Good luck..

Steve
s/v Good Intentions