It's cooling off right now. I'll fire it back up again in a bit and
check it out.
I'm pretty sure the resistors are wired in parallel. It was heating up
fine until this morning. (For what it's worth, one wire goes from the
relay board to one terminal of the first heating element then to a
terminal of the second heating element. The other wire runs from the
second heating element back to the first heating element, and then
back to the relay board).
Looking at the connections again, I'm wondering if the high-temp
solder I used wasn't high-temp enough. It's looking a little
tarnished. When the thermistor was loose, I probably hit 250C before I
fixed it, which could have broken my connections. I'm going to see if
I can find some high-temp solder in San Francisco someplace tonight,
resolder it tomorrow, and try it out again.