Find the trainer switch on top of the radio and look on the inside to verify that it is a three-pole switch (probably spring loaded one way). With the trainer switch in its normal position, the PWM signal comes in on one side and goes back out to the RF deck through the center pole. With the trainer switch pulled the other way, the PWm signal comes in from the other radio on the other side of the three-pole switch and goes back out to the RF deck on the center wire. You need to pull the PWM signal from the center pole and feed that to FMS through the parallel or serial interface you build.

An example is on my web page at:
http://members.fortunecity.com/chris...fwiw/fwiw.html

Chris