Wiring and Installing the avionics

Wiring the aircraft (batteries, starter relays, alternators, ignitions, switches, etc.) and wiring the avionices (Garmin G3’s, Garmin G5, Garmin GTN750, etc.) are the two main “groups” of wiring tasks.

Group one (Wiring the aircraft) is not all that difficult. There is a lot of information out there about this. I did the majority of those tasks myself.

Group two (Wiring the Garmin and other avionics items) is a very detailed and time consuming project, so I hired a fellow pilot, Jon Thocker, who had already wired 10 or so Garmin panels. This really sped up the project, and saved me from a steep learning curve. Still, I read (poured over!) all of the installation manuals and pin out diagrams so that I could create a list of desirable functions and features in my panel.

For a couple of examples: I have learned from experience with my Lancair Legacy gear system (which is mostly identical to the V-Twin system) that a really nice (almost mandatory feature, in my opinion) is to have gear up and down pressure gauges. With our new avionics suites like the Garmin G3X, there is no need to install physical gauges. Rather, it’s a matter of researching and obtaining suitable pressure transducers and routing their outputs to the display.

Another example is similar: I knew I wanted a CO detector for my airplane. It’s probably not so critical in a “pusher” airplane, but I still thought it was a good idea. Once again, research and obtaining a remote CO transmitter was accomplished.

There are quite a few examples like this – TOGA button (sets up the flight director for takeoff, or initiates a go around if on an approach – when using the flight director and/or the autopilot), cameras, USB ports, cabin lights, temperature sensors, etc. By being intimately familiar with the Garmin installation manuals and the various pin outs, I was able to detail not only the items I wanted Jon to wire into the harnesses, I was able to even tell him which pins to use. This really helped him get the job done in a reasonable time.

As a strategy to avoid electrical noise, we ran the main power cables down the right side cabin duct. We also ran the other avionics wires in this duct, using shielded wiring. The radio and transponder RG400 (which is also shielded) cables were routed through the left side cabin duct. Finally, such things as cabin led lighting and headset jacks were routed down the center console. Time will tell if this is a good strategy.

Wiring the circuit breaker panel: I divided it into a Main Buss, Avionics Buss, and a 12 volt Buss. The Master Switch turns on both the Main and the 12 volt Buss via separate relays. It also enables the Avionics Buss switch.

Once we determined which items would be mounted on the canard, we made hard points to attach them. Such items as GPS antennas, GAD27, AHRS, backup battery, trim power booster, and auto-pilot actuators went here. I chose to fully populate the canard space as a strategy to put as much weight in the front of the airplane as possible (due to having the AC in the tail cone).

I made a custom mount for the aft items. Space was a little tight as the air conditioner box took up a lot of space. Such items as auxiliary warning system, voltage regulators, current limiters, amp shunts, temperature transducers, starter relays, aft fuse block, aft Ground Buss, and aft Power Buss were installed here.

There are three temperature transducers for my central warning systems: left spar temp, right spar temp, and ac condenser fan outlet air temp. I also have two additional spar temps that are wired to the G3X displays. The G3X spar temps are to protect against any event that might cause the spars or, indeed, the engine compartment to experience higher than normal temperatures – a good thing to know, especially in a pusher configuration. The spar temps for my central warning system serve the same purpose, but are also positioned near to the PMags to ensure they are getting adequate cooling. The ac outlet temp is to ensure this unit doesn’t overheat for some reason. As it’s inside the tail cone, the pilot might not learn of such an overheat until it’s too late.

I used Plane Power alternators and also Plane Power voltage regulators. I wanted the Plane Power alternators because of their reliability and good reputation, but also their lighter weight – perfect for rear mounted engines. While I wanted 100 amp versions, since I have a 24 system, I had to jump up to the 150 amp versions. They claim that these will output 130 amps at 1,000 rpm! Just perfect for my electric air conditioner which draws about 35 amps, but even better for my electric heaters which can draw 35 – 45 amps each. Everything else in the airplane draws about 10-12 amps in total.

I also chose Plane Power voltage regulators as they have a perfect feature for a twin engine airplane. And this feature really simplifies designing your electrical system. These VR’s can “talk” to each other. One is the Master. The other is the Slave. This way, they can balance the outputs from the two alternators. This allows the builder/designer to connect the alternator outputs to the same power buss with no issues. Just perfect. If one fails, the other continues to provide power. If both are working, their outputs are balanced.

One buss, two power sources (well, three if you count the batteries). Simple. I like it. Also the G5 has it’s own backup battery and GPS. It can even fly the autopilot. I have an additional backup battery for the other Garmin items like the displays, audio panel, transponder, and so on.

My “main” battery system consists of two large 12 volt batteries (Odyssey PC925’s) connected in series. These are big and provide a lot of reserve power. You need the weight up front anyway, so might as well have that extra weight provide electricity.

On the left is Jon Thocker, my pilot buddy and airshow pilot. He helped me wire up the Garmin avionics suite. Sadly, a few months later, he died in an airplane accident as he was practicing for one of his renowned air shows. He was truly a great guy, and he did an awesome job helping me with the wiring.

And on the right is Andrew Burrows of Aero Safety Systems. As I was one of his first customers, he volunteered to help me install his system. He flew all the way from his home in the UK! He wanted to determine what, if any, issues might be involved with the installation. It all went really well, but he did make some upgrades to some of his specifications as a result. This was certainly a win-win situation. Frankly, he “worked like a dog” for a few long days as he joined us for the wiring “fun”. I will be forever grateful for his expert assistance. And I highly recommend his products.


I purchased my avionics from SteinAir. They assisted me with the panel layout. They already had the panel set up in their CAD software. They also provided a complete wiring diagram. And they not only cut the aluminum for the panel, they arranged for much of the hydro-dipping finish work. Great guys. Great company. Super helpful. I highly recommend them.


And there is a lot more! 🙂

Internal lighting, external lighting, USB outlets, O2 outlets, etc. Take a look at the following pictures for more. Such things as batteries, master relay, center console, custom overhead panel with EI Commanders, heater wiring relays, etc.

Functional Wiring Diagrams

Air Conditioner Wiring

Continue to: Engines

Back to: The Completion Center