OK, so no mechanical oil pressure or water temp. They are electric.
I don't know what components are left over from 1939 or if the electrical has been updated and to what extent.
In general: To be safe and update to more modern standards:
1. Everything needs to be fused. Even the power wire to the fuse panel. I don't know if you have a fuse panel or not.
2. Everything has a switch, as you know.
3. Dash lighting power usually comes from the headlight switch and sometimes has a dimming function. Headlight switches have fuses and thermal overload protection built in. The bulbs can be wired in series.
4. The ignition switch input power (bat terminal) is fused from the fuse panel. The gauges, other than ammeter, are powered by the ignition switch "on" terminal and can be in series.
5. Series is what you are asking to do to save wire.
6. Components who have their own switch (I.E. heater fan motor) need to be fused before their switch.
7. Headlights and tail lights are fused at/by the headlight switch, usually. As said in 3.
8. Use fusible links for main power wires from battery. Not speaking of positive battery cable.
9. Brake and turn signal filaments are controlled by a turn signal switch.
10. Dome and horn are a little different wiring. Their switches operate a ground path instead of switching power like all the other switches.
You didn't ask for all that but it's just for you to contemplate.
I don't like ammeter style wiring method. I like voltmeter style.
