manufactured both battery cables out of 2 gauge welding wire, with ring terminals swaged on with my nifty new molex big cable crimper. This is the only aircraft tool I've ever seen where the instructions have you hit the tool with a 2 lb hammer in normal operations :) I wanted to make the positive cable as short as possible and had originally made one about 10" long. Welding cable is so flexible, I though I could make the bends around the battery box and possibly use one of the battery box mounting bolts to anchor an adel clamp to. Unfortunately, I could see a potential for the cable to rub on the corners of the box even with a clamp. The radius is just too tight. So, I scrapped that plan. Fortunately, I had bought a couple of feet of wire, as well as some extra terminals, so I had enough extra for a second attempt. This one is 12" long, and is well away from the battery box top and bottom. I'll eventually install an adel clamp to a nutplate on the firewall about midspan, but I the correct size adel clamps are on backorder at Airparts and won't be here until next week, so there's no rush with that. For the negative cable, Vans OP-30 has you upsize the second rivet hole down from the top starboard side of the firewall cutout for a -4 bolt and attach the ground there. With all my fancy avionics, I'm going with the forest of tabs that everybody uses. I'm putting it in a common location, centered between the F-7108 center fuselage rib and the F-7107-r right fuselage rib, and 2.5" up from the angle that runs across the firewall at the top edge of the cutout. Based on that, I turned Vans original location into a mount point for a adel clamp by installing a #8 nutplate in that location. The forest of tabs that I got from SteinAir comes with a big brass bolt to use as a mount point. It goes through the tab, through the firewall, then a washer and jamb nut, then a washer, battery cable, another washer, and then the main nut. Couple of issues with this; Issue 1- It has a hole in the middle for another mounting screw, but I elected to not just have the whole other half of it hanging, so I drilled and installed a -3 nutplate on the other end for an AN3 bolt. Now its secured by a 5/16" brass bolt on one end and an AN3 bolt into a nutplate on the other. It's overkill from a structural standpoint, but it's about the best electrical connectivity back to airframe ground I can figure out how to implement. I think that Vans design just has an airframe ground to the aforementioned AN4 bolt and a ground strap from the engine to the firewall, but I think I'll likely run a ground cable from somewhere in the general vicinity of the starter back to the battery or to the firewall side of the brass bolt as well, so that pretty much everything will have a copper wire ground path back to BATT negative rather than running through the airframe. Hopefully that will encourage all the electrons to play nice and eliminate the potential for gremlins in the engine sensors. Issue 2- If you look at the stackup on the brass bolt that I listed above, you'll notice that there's no locking device whatsoever. Yeah, the bolt it clamped to the forest of tabs and the firewall with a nut, and yeah, there's another nut on top of it, but it anything works loose in that stackup, I could start having intermittent or weak ground issues with all the avionics, and main ships power as well. Not as catastrophic, but certainly annoying, if I ever have to take this thing apart after the plane is finished, it seems likely that the bolt could just start spinning in the hole before the top bolt comes loose. I believe this stackup needs a split lock washer under the first nut, squeezing on the firewall. however, I don't have one in the correct size right now, so I'll have to acquire one. or maybe two. I'll ponder this for a while. I also wanted to do a little more under the panel before I started pulling wires, so I played around with routing for the heater cable. This led to discovering Van's OP-26 that shows where to drill a hole through the firewall stiffener etc. I accomplished this, then started thinking about how to run wires through the tunnel and up the cabin side of the firewall. This led to needing to install the heater diffuser cover in the cabin to visualize things, which led to temporarily installing the firewall recess, which led to installing a couple of nut plates in the recess to attach the cover to later...you get the idea.