The Cozy firewall is a non-magnetic stainless steel sheet over Fiberfrax. A lot of planning goes into the layout of both the engine side and the cabin side. The engine side is designed for ease of service, engine layout and clearance. The cabin side is about short runs, logical flow and ease of service. A lot goes on the cabin side of the firewall. I made up a template and did the layout of components – battery, contactors, relays, battery and engine busses, et al. Cables and connectors come up from the lower corners, then run on the outside of the curve. I aim to have the runs to alternator and starter use the passthrough fittings below the right side of the picture (pilot side). The electronic ignition runs will use the passthrough below the left side of the picture (passenger side). Ground - Engine side. The alternator grounds through its case to the engine mount. A #2 AWG cable connects an engine case bolt to a brass bolt passing through the firewall and becoming the cabin ground. That brass bolt is the fat point ground on the firewall, connects to a non-magnetic steel firewall by direct contact. Also on the engine side is a supplemental ground for the starter - it grounds through its case to the engine, and also through a #2 AWG cable to an engine case bolt. Grounds - Cabin side. The busses are grounded by a brass bolt / fat point penetrating from cabin to engine side of the firewall. On the cabin side it is connected to battery negative with a #10 AWG cable. The starter contactor grounds, through two short brass bolts passing through the firewall. A #10 AWG cable connects one of the bolts to a field of tabs. The field-of-tabs has a brass bolt pass through to a second field-of-tabs on the engine side of the firewall. Power - Engine side. The _normal_ power source is a 60a alternator (B&C LX60). Consistent with the Nuckolls schematic "Z101b", a #8 AWG wire runs from the B lead through a lower right side access port to the cabin side. The field wire is a brown plug on the forward side of the alternator, with a lead running alongside the other power wires, throught the lower right side access port. The _auxilary_ power souce is a permanent magnet generator (B&C SD-8), made to fit the vacuum pump port on the accessory case with a rated output of 8.4a at 3500 rpm (2700 engine RMP). The Nuckolls schematic allows for a generic aux alternator, while his text endorses the B&C generator. I followed the B&C instructions for the SD-8 generator, so that the aux power wiring differs slighting from the Nuckolls schematic (see below). In the future I may choose to replace the 8a with the 30a version from Monkworkz (also mounted on the vacuum pad). See https://monkworkz.com/product/mz-30l/ . Power - Cabin side. The 60a alternator is fused by a 12AWG fusible link used next to the contactor connection (see schematic detail below). The alternator regulated by the B&C LR3D-14 'controller', consistent with the template schematic Z101. In the detail photo below, the LR3 is the silver box below the red tray. The LR3 is 1) a linear regulator, generating no audio or radio noise; 2) a solid-state, crowbar over-voltage protection circuit; and 3) low-voltage monitoring and warning (yellow light flashing at the panel). The controller also has overvoltage protection, a capacitor to smooth the current delivered and a relay to switch between main and backup alternator. At the panel a clear-yellow warning light that will illuminate if the crowbar over-voltage protection module is tripped or when the alternator switch is left off. Above the B&C controller is a red tray. It holds a regulator for the backup alternator (B&C model PMR1C), which is a _switching_ series rectifier with a rectifier bridge, adjustable solid-state regulator circuitry, and built-in heat sink. At full load (8.4 amps output) it "rejects" ~20 watts of heat. Per Nuckolls, "The power-path components depend on thermal conductivity of the potting compound for heat rejection. The rectifier/regulator's service life is tied to optimizing thermal management." The installation instructions warn against mounting to a composite surface - the red tray is an aluminum platform for the unit. (On an aluminum tray at 8a output the B&C test results point to a max temp of 125F. Since aux power operations are last only until a safe landing, the heat seems a reasonable risk.) The large blue capacitor below the red tray has two functions – it presents the SD-8 generator with the starting polarity, and it smooths out the noise that comes from a switching regulator. Also on the red tray is a relay, switching the alt aux alt bus feed to the main bus. There are diodes protecting each of the relays and a diode bridge protecting the engine bus (the silver box above the red tray). [I'm not overly confident that 8a of backup alternator can do the job. There is an alternative for a pad-mounted backup - the Monkworkz 30a. I'll check it out at SnF and can make a final decision after wiring the SDS system.] 4/16/2023. This evening I finished the power lines described above. It continues to seem nutty to have the heaviest cables (#2 AWG) used for the very short term task of starting the engine, while much lighter cables (#8 and #14) carry the power from the alternator and generator. =============================================== Lots of learning. I had used several methods to secure fasteners (rivet nuts & click bond studs) to the cabin side of the firewall: marine adhesive, epoxy & BID, flox & BID, marine adhesive on aluminum plate holding an installed rivet nut, et al. I decided to test the security of the components. Results were terrifically inconsistent, with some click bond studs easily twisted off with pliers and others pried off with a paint scraper and elbow grease. Bottom line, I need to find a new way to secure components to the cabin side of the firewall. The new approach is to build the system on the bench, firmly securing everything to a sheet that can then be attached to the firewall, using the existing holes. This will sharply reduce the number of firewall penetrations - I won't be drilling two dozen holes to secure everything. I then prepared such sheets using stainless steel, a coreplast board and my own layup (1/2 foam with 2 layers BID each side). The 22 gauge non-magnetic stainless steel was heavy (3 lb 13 oz). Coreplast was 2 lb 4 oz, my own layup 1 lb 14 oz (before trimming). 22 gauge aluminum was 1 lb 13 oz (after trimming) and it's easier to set fasteners in the aluminum. I'll go with the aluminum.