Most autopilots use ARINC 429 A & B connections to GPS.
I have GNC250XL, but it has the same pinout as the 300XL.
J101, pin 16 is ARINC 429 out A and pin 15 is ARINC 429 out B.
Is the GNC300 the same unit as the 300XL? I think it is.
GNC300 wiring diagram here. It has plenty of outputs. J1 - Pin 19 for NMEA, and ARINC ins and outs. Jim are you looking at the install manual and you just dont know what you are looking for? http://static.garmincdn.com/pumac/GNC300TSOGPS_COMM_InstallationManual.pdf
Some autopilots like the Navaid use a +/- 150 mV lateral steering signal like used to drive an analog CDI. Perhaps this is the signal you are asking about.
Pins 1,4 on 300XL connector J101 should provide a signal of this type. If you put a DVM across these two pins you should see 0 mV when the CDI is centered, 150 mV when the dev bar is 5 dots to the left and -150 mV when the dev bar is 5 dots to the right.
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Thanks for the responses guys. I guess I should have explained my question a bit better. I removed a Navaid AP (driven by my 300XL Garmin and Nav radio)and replaced it with a Trio. I listed it on the classifieds and someone wants to know if I have a converter(decoder/smart coupler?) for it. I just snipped the wires to the head and don't recall seeing anything under the panel that looked like it would go with the AP head. So I was just wondering if there would be one involved in that set up or not. (Before I go diving under the panel again to give it another look).
