The plot thickens...
First, when I said the lights haven't "worked for some time," I meant that they have not worked for as long as I've had the plane (~1 year). My father, who I got the plane from, swears they worked, but can't remember for sure. He says it checked out each time during annuals... but Glareshield was noted INOP on my annual.
Both Panel and Glareshield wires have 24V power - I checked today per RoundTwo's suggestion.
However, I found that the switches were cross-wired (you will see this in my pin diagram here in orange highlight, when compared to the Light Control Box schema):
The Panel switch has the panel power, but wired to Glareshield out
The Glareshield switch has glareshield power, but wired to Panel out
So - the behavior seems to be: no light on either glareshield or panel, but the map light under the yoke stays on all the time no matter what.
What I plan to try next:
Cut wires LP07E20 and LP03C20 and cross+crimp, then try the old control box.
If that doesn't work, connect LP07E20 (circuit), LP02E20 (positive), and Green / White-Blue / LP11D20 (ground) to the new dimmer and see if that makes the Glareshield work.
If so, connect up the other dimmer. I'm not quite sure what to do with the GPS Annunciator wire, as it is going through some fancy box on the circuit board, but will try to wire with the circuit.
If that doesn't work... time to fly it to my mechanic (during the day).
Finally, I do not plan to install the inline fuse, as the kit recommends, since I have breakers.
Sound like I'm on the right track?
Thank you for all your help so far!