The replacement controller came in the mail, but I was still having problems turning it on. The battery set would read 66 volts when charged, but would read 15 volts under load. And the charger would flicker when I tried to plug it into the set.
Turns out the set of batteries have a few corroded terminals, which I fixed easily with a wire brush. After that was figured out I got the controller mounted and all of the wiring cleaned up.
And then I gave the floor pan a coat of vinyl dye and cleaned off one years-worth of dirt.
The replacement DC-DC converter came in the mail too. But I'll have to wait to install it until after the LED headlight is done.