Tell me more about the harness that controls all these gauges... Is it a home-built system, or did you purchase it? I like the extra gauges, but I'm not sure how you're controlling them all through that harness...
The harness is all home built, on the other side of the terminal blocks there is a stereo ISO plug which connects the dash to the car loom (which has also been modified).
The vacuum gauge is mechanical so it gets power/ground/illumination, the voltage gauge again needs power/ground/illumination and finally the oil pressure gauge needs power/ground/illumination/pressure, so really the pressure is the only one that needs controlling via an electric signal, you can see the wire as its the only green wire on the dash. This connects through the ISO plug to a sender in the engine bay.
I have tried to make a circuit diagram below showing where all the wires go. It might explain how the electric side of things work. I have removed the mini pcb from the clocks and then soldered/crimped to the fuel/temp/tacho and the bulbs.
Ambitious... So you can just unplug the entire dash for removal. Kudos - that's an awesome idea. If I were to ever put in a dash board, this is how I'd do it. Nice work!