Custom Electrical Installations for Aircraft: First Power Up

Posted On January 10, 2025

I’ve spent the last few weeks installing all the electrical provisions, ramping up especially the last few weeks over the holidays to reach a safe-to-apply-power state. I successfully powered up the airplane for the first time this past weekend and it was nice to finally see the panel all lit up. After configuring the G3X system, it successfully communicated with all the components connected via CAN, RS232, HSDB, and even the Rotax FADEC CAN.

One of the big blockers to getting to this state has been the installation of the custom climate system, which is now mounted in the partition between the firewall and the IP subpanel. The wires you see going to the climate system housing connect to temperature sensors and stepper motors that open and close flaps, redirecting air where needed.

With the climate air housing mounted, I was able to turn my attention to terminating all the wires that go to the components mounted to the subpanel section. The subpanel itself doesn’t have enough room to mount everything, and it’s a pretty thin webbing (only 0.020″ thick) so I designed and built custom rails, hat sections, and brackets to mount these components, including:

• 2x Garmin GSU 25 ADAHRS
• GTX 45R Transponder
• GEA 24 Engine Indication System
• GMA 245R Remote Audio Panel
• GAD 27 Flap/Trim/Discrete support
• 6Ah standby battery from TCW
• Climate system control module

All of these components connect via the two large interconnect receptacles at the center of the subpanel, so that the instrument panel can be removed (relatively) easy.

After a few days work, I had most of the GEA24 and GMA245 wires terminated, and I closed off the connector backshells.

I have a pair of ADAHRS computers and an emergency avionics battery mounted atop a hat shelf that was carefully mounted to keep the ADAHRS aligned to the aircraft axes. I was able to achieve and alignment error of <1°.

I needed a place to connect a few auxiliary electrical items, so I bought a Littelfuse HWB12 power distribution module (PDM), which uses the same ISO280 pattern as the Bussman modules on the main power distribution panel. To this block, I ran a +12V always-on circuit from the main battery, which will provide power to the lighting system, so that cabin lights can turn on regardless of the main battery switch position. The cabin lights are controlled by what I call a “Comfort Lighting System” controller on the panel, which runs in a very low power mode until triggered to wake up.

I also ran the main shunt sense lines from/to this block via 1A fuses before going over to the GEA 24, as required in the G3X installation manual. The shunt senses the current flow from the battery to the main electrical bus.

Unsurprisingly this Littelfuse PDM required different contacts than the Bussman modules; this application required TE MCP 2.8 contacts. Luckily they are similar enough to Delphi Metripack 280 contacts used on the Bussman so that I was able to use an existing tool to terminate the contacts.

The next photo shows the main power distribution panel, which contains circuit breakers, relays and fuses to distribute power and control circuits. None of the high current devices (e.g. pitot probe heat) are directly powered by switches on the panel; instead the switches activate relays in the PDP.

The next few photos are the same view taken a few days in succession. It doesn’t look like a lot happens, but there are several wires being terminated and checked each day. I also bundle and secure wires as I go using zip ties and a variety of mounting blocks to hold the wire bundles in place.

It took another day or two to complete pin-to-pin continuity checks to reach a state of safe-to-apply-power. After verifying all the fuselage-side wiring, I was ready to marry the panel to the plane. In preparation, I removed all the heavy items (G3X displays). The large holes in the panel also make it easier to access the connectors that need to be attached once the panel is in place.

I mounted a loudspeaker on the instrument panel and located it so that it would fire up through the mesh panel that is pre-installed by Sling on the dash assembly. This speaker plays alert tones, and can also be used to listen to the radios without headsets.