With OctoPrint talking to the Klippy host software on the Pi talking to the Klipper firmware on the Spider mainboard and the Voron’s LCD lit up and control panel working, I could see that the firmware was able to read hotend and platform temperatures and I used the printer’s control panel to test each of the two heaters. The heaters worked; but I noticed that when heating the hotend, the part-cooling fan came on and the heat break fan didn’t. Probably the fan connections were swapped?
I’d wired the printer per Fysetc’s diagram for this printer on a later revision of their Spider board because it was the only diagram I could find at the time and I wanted to be able to use a sample configuration file as a starting point rather than do the whole pin configuration from scratch. Tempting though it was to just swap the two fan plugs on the mainboard and be done with it, I went back to the wiring diagram from the Fysetc Spider board GitHub page first for a closer look.
Oh. Oh, I see. I had previously noticed that Fysetc had labeled both of them as 4010 fans; but I hadn’t noticed that they had swapped the labels of which fan served which function. I had originally connected my fans by tracing which function was connected to which Spider port; but with the functions swapped on the diagram, my wiring was swapped on my board. I now changed my wiring to match the Fysetc diagram’s intent (and the sample printer.cfg‘s configuration) and noted the error in the wiring diagram here for later reference. The fans now behaved as they should.