After installing a "trio" of gauges (temp, oil press, volts), the dash lights no longer work.

No fuses in the block are blown. Turned on the headlights and all the electrical works except the dash lights (which previously lit up brightly). The light switch and rheo-stat worked well previous to my electrical exploits.

There are a total of four electrical connections made so the trio of gauges can work properly. Two grounds and two switched power connections.
As my F-85 is not optioned very well, there are an abundance of extra connectors hanging off the stock wire loom under the dash. I found one switched positive connection and one ground location hanging off the stock loom.

The other switched power source is coming off the fuse block so the lights in the trio of gauges will work when the headlights are turned on.

After discovering the dash lights were not working, I reversed all the connections made with the trio gauge install and the dash lights are still not lighting up.

I'm at a loss.

Besides a fuse, is there anything which could make my dash lights stop working?

 

Double check the fuse. I had the same problem. After going around in circles chasing things. I took out the fuse instead of looking at it. It looked good. But when I got it out the metal end had come unattached.
If it is good start disconnecting wires one at a time and see if you can trace the problem.

 

Disconnect the "trio" and see what happens from there.

Buying a test light might help if you know how to use one.