Having spent hours planning and documenting the proposed avionics wiring, the last few weeks have seen me attempting to actually create it.
It’s been a lot easier with the fuselage on its side, allowing good access with only the occassional expletive when routing wires.
It’s amazing how small objects just dematerialise when dropped … resulting in frustrating minutes peering inside to find the blinking thing!
Since everyone’s wiring is bespoke, it’s of relatively little value to look at other people’s wiring. So what follows is intended to merely give a “flavour” of my avionic wiring so far …
The Garmin G3X system has a CanBus data link, and the manual is very specific about best practice.
I’ve followed the advice as closely as possible, using Raychem S01-01-R & S01-02-R solder sleeves to splice the wires and link the wire screens.
As I’ve extended the CanBus I check for continuity and most importantly no shorts between the screen and individual wires.
Since the GMA245 Audio Panel is at the bottom of the stack, that’s where I started wiring the connectors.
Where possible I assembled the connectors on the work bench, but eventually it has to be done in the aeroplane … this is because lots of wires eg power, headset, mic & Joystick PTT are in the plane waiting to be connected.
Garmin recommends Silicon Fusion Tape to protect the wires under the cable clamps.
This chap has 4 connectors, with lots of pins. But many are unused depending on the installation equipment, so it’s not too daunting.
This shows the “Configuration Module” wired into one of the connectors. This module remembers all the settings when the power is removed.
There are several power/ground pins, and the power requirements for some of these mean 18awg wire. But the DSub pins are HD, so will accept a maximum of 22awg … hmmm??
To get around this Garmin allow you to split an 18awg wire into 3x 22awg wires, which will fit into the necessary pins.
I’ve used red wires for power, and black for grounds.
Wires not tidied yet, but coming togethger. I’ve used P-Clips to anchor and route the wiring.
The GTN650 has a fan on the back for cooling, and this is wired into pins in one of the connector blocks.
This has 4 connectors, and 2 of them house the sensor wires to the engine.
So those will have to wait until the engine is installed.
This unit has several “Disrcrete” pins, which can be used to trigger various functions eg a Parking Brake caption on the EFIS Screen when active.
Some of these pins need a 5K PULL UP RESISTOR … no, I had no idea what this was all about either!
These inputs work by either receiving a ground signal, or a 12V signal. If there is no input to the pin, ie “floating”, and they are configured to be “active” when grounded, then the pin is raised to 12V by connecting the pin to a 12V supply via the resistor. The resistor means very small current flows between the pins.
This all means that there is a clear difference between “Active” and “Inactive”.
Anyway, I needed two of these inputs, so I soldered the resistors in a “zigzag” arrangement for strength, with heat shrink tube to finish.
This unit distributes the power to the trims, flaps & lighting.
The 18awg lighting/flap wires are connected with ring terminals rather than pins.
As mentioned in an earlier post, here in the UK the traffic conspicuity situation is still work in progress.
So we’ve fitted an Air Avionics Air Traffic system, which detects ADSB, Mode S and FLARM traffic.
Hence 2 Flarm antennae, 1 ADSB antenna, GPS and static pressure all need to be connected … phew!
I’ve fitted a TRIG TY91 remote radio for Com 2. In Europe we have 8.33KHz spacing, and Garmin at the moment do not supply a remote radio with 8.33.
The Trig connects to the Garmin G3X via RS232 … seen here with the wire screens grounded via pins.
The Trig TY91 is connected to a control unit in the panel, a TY90.
Here’s this connection being wired on the bench.
At every stage I’ve been checking continuity between the various pins, and also double checking I’ve got the correct ones linked!
And also making a note on my wiring diagrams to show which wires have been checked.
I made a test harness to extend the reach of the multimeter. Sounds fancy, but it just connects the multimeter leads to long lengths of 22awg wire …
… with a crocodile clip and pin spliced on the end. I’ve found it useful to insert the DSub pins into the various connector pins whilst linking to check continuity.
I spent a day routing and trimming the antenna cables to length, and then attaching the connectors.
I did leave some leeway in cable length, but not much since I didn’t want loops of RG400 cluttering up the harness.
Quite tense, since if the connector attachment goes wrong …. !!!
Anyway, so far so good … I think?
I won’t really know until it’s all switched on!
But all the wiring is now complete in the “Avionics Bay” forward of the subpanel. The next stage is to wire up the units in the instrument panel.
I’ve allowed myself a mini “Happy Dance” : )