After much trial and tribulation I have finally finished a really functional Ternary Sum gate. Following are two pictures. The first is the prior incarnation of the Sum gate that barely functioned. The second is the slightly simpler and entirely reliable Sum gate.

Here's the awful one:

And the one that actually works:

As mentioned before, the output is the 1-trit sum of two input trits. The carry is handled by the Consensus gate which has already been published previously. That means I now have every ingredient necessary to produce a ternary ripple-carry adder. However, at this level of integration it won't be trivial. The Sum gates still take a surprising amount of board space. Both of the two pictures above were the result of compacting the components down so that every single row was utilized. The final result still takes up a 1/2 sized solderless breadboard for a single gate.

The improvements in functionality are due to the fact that I replaced most of the diode logic with pass transistors. This would have increased the footprint of the gate, but I then changed over to replacing every comparator that could be replaced with a transistor. This reduced the footprint enough that it is just barely smaller than the original design, but is now fully functional.

As a note, that funky breadboard is one of the 5e boards I favor over traditional solderless breadboards. I've arranged the power rails such that they mimic a particular prototyping board that I think I will use when I switch from experimentation to actually building something. The board I intend to use is the SB1660 from Busboard Prototyping Systems and was selected because of its many power rails to carry my -5, -1, 0, 1, and 5 volt rails.