Tankerpilot75
Well Known Member
I’m upgrading my old GRT WS EFIS units to the GRT Horizon EX units. I’ve had to run new wiring for the warning audio output from the EX units to the Garmin 340 intercom system (WS units didn’t have audio warning outputs).
I discovered during this process that there was already wiring to the Garmin 340 (pins 31 - Alt Warning In and & 32 Alt Warning Return). These are the two 340 pins recommended for this purpose. Unfortunately I have no clue what these two existing audio wires are connected to.
An airport friend ( who is an engineer and A&P/IA) suggested I just add my new audio warning input wiring to the existing two wires going to the Garmin 340 pins but in addition add 390 ohms resistors (covered in shrink wrap individually) to the two positive wires feeding pin 31. I asked GRT tech support about this but they never responded.
My questions:
1. Has anyone else attached two audio inputs to the same audio input pin?
2. Why are 390 ohm resistors required on both positive lead ins to the Garmin 340 pin 31?
I discovered during this process that there was already wiring to the Garmin 340 (pins 31 - Alt Warning In and & 32 Alt Warning Return). These are the two 340 pins recommended for this purpose. Unfortunately I have no clue what these two existing audio wires are connected to.
An airport friend ( who is an engineer and A&P/IA) suggested I just add my new audio warning input wiring to the existing two wires going to the Garmin 340 pins but in addition add 390 ohms resistors (covered in shrink wrap individually) to the two positive wires feeding pin 31. I asked GRT tech support about this but they never responded.
My questions:
1. Has anyone else attached two audio inputs to the same audio input pin?
2. Why are 390 ohm resistors required on both positive lead ins to the Garmin 340 pin 31?