The electrical system and wiring is my favorite part of the construction process. Anyone interested in experimental aircraft electrical systems should absolutely be aware of Bob Nuckolls work. I highly recommend a thorough reading of his book, The Aeroelectric Connection. The book, and much other information, can be found at his web site... www.aeroelectric.com. Bob has found sources for many parts, tools, and supplies needed in crafting experimental aircraft electrical systems also which are sold by his friends at B&C Specialties.
Typical GA aircraft electrical systems were designed decades ago and don't reflect much of what has been learned in the intervening period. There are a couple of concepts core to Bob's recommendations that I think should be incorporated into any experimental aircraft electrical system. The first is that of single point ground. I am an absolute believer in this and have much personal experience supporting the validity of this approach. I built my RV-8 with single point ground and never had a bit of noise. One of my pals who also built an RV-8 at the same time did NOT use single point ground and almost every electrical appliance in his plane makes noise. The second is that NOT routing the alternator output through the firewall to the typical master breaker, but rather routing it to the hot side of the starter contactor which in turn feeds the battery directly. A supply wire is then run to the main bus from the master contactor which is already behind the firewall — you end up with fewer firewall penetrations and shorter fat wire runs. Bob's book will give you the whys and wherefores of all this, give it a read, it works.
Regarding multiple buses as featured in most of Bob's sample wiring diagrams, just be sure that you thoroughly understand how they work and flow so you can deal with any malfunctions that present themselves. My concern is that with three or four buses, some interconnected and some not, many pilots wouldn't be able to manage problems quickly during an in-flight situation. As with most things in aircraft, keep it simple so you can understand what's going on in any scenario and therefore properly manage it.
Consistent with Bob Nuckoll's philosophy I will be using blade style automotive fuse blocks rather than "acres of breakers", one block for main bus items and one for the avionics bus items (supplied by an avionics master breaker/switch). These blocks are strategically placed so that I can get at them in flight by simply reaching under the panel. I can't necessary see them, but can get at them if needed. Anything you need to be able to pull power to quickly should not be put on a fuse but rather on some sort of a breaker that is accessible. There are a couple of breakers on the panel as opposed to fuses so that I can pull them if needed (alternator field supply, EFIS power supply).
Today's instruments and avionics all seem to have brain boxes that go with them. An RV-3 is such a small environment that locating such boxes quickly becomes an issue. Fortunately there's a perfect space where the fuselage fuel tank was formerly located. I constructed a shelf to which I've attached all my various brain boxes using both the top and bottom surfaces. As you can see in the early picture, the shelf is integrated with the center console I built and also holds my two fuse blocks on the crossbar.
Aft battery mount
I initially opted to mount my battery between the two floor ribs just forward of the main spar. I had constructed a neat battery tray and hold down that fit into that floor console area nicely. Unfortunately
after weighing and flying the plane I determined that my CG was just too far forward and the battery was about the only thing that could be moved that would have any effect on it. I therefore relocated it to a position just aft of the seat. CGwise I could have mounted it further aft but I didn't want to interfere with baggage area that much. Also, while I did want to move the CG too far aft, I still wanted enough baggage capacity for my aux fuel tank. This location worked out as a good compromise. I eliminated the forward part of the baggage floor skin and am using the forward tank mount crossbar to keep baggage items from interfering with the flaps and battery. Leaving this open lets me inspect the rear spar, flap mechanism, and battery and cables easily.
I am building this as a day/night VFR ship and therefore have added all the requisite lighting including the Whelen combo nav/strobe light package. I prefer separate strobe power supplies in each wing so the high strobe voltage cable doesn't need to be run from a central power supply. I also have Duckworks wing lights, HID in fact, and fairly comprehensive interior lighting. All lighting is controlled from a switch panel on the right side of the cockpit.
I am installing a TruTrak Digiflight IIVS.
For my thoughts on why I selected such a capable unit, and what a priority it is, see my comments on the panel page. Regarding servo installation, TruTrak has a selection of various servo mount kits but of course none are for the RV-3. I used the RV-4/8 pitch servo mount and the RV-7/10 right wing mount kit. Both worked well with only minor adaptations required. At first I wanted to locate the roll servo in the cockpit under the seat but quickly realized that the mixer box mechanism and lack of space both made that unrealistic. I then went with the right wing aileron bellcrank location using the RV-7/10 right wing kit. One of the brackets need to be modified, but otherwise it went right in. The pitch servo installed easily at the elevator bellcrank location using the RV-4/8 kit. If you are building your fuselage (rather than retrofitting), just leave the pieces of angle that form the baggage compartment floor ribs longer.