I think of four electrical systems when I wire.
1. Ignition/starting
2. Charging
3. Lighting
4. All other components/switches
Typically most every component should be fused with it's own fuse panel fuse or a fusible link. With your 12V/V8 system, I do not know what headlight switch you have. Some headlight switches have a fuse at the power input. Some have internal thermal breakers/fuses.
As Wrenchbender says: Headlight switches have two power inputs. One for headlights and one for basically every other light. The one for the headlights connects power to the dimmer switch when “headlight” 2nd position is clicked.
The other power input, which usually comes from the tail light fuse, switches power to tail lights and parking lights when 1st or 2nd position is clicked. The rheostat dash light dimmer section sends power to the dash light fuse at variable output voltage. All depending on position or rotation of switch.
Again as Wrenchbender says, the headlight switch is unique. It has, sort of, several switches within. So for any "position" of the headlight switch, it is connecting power to light circuits. You must wire the headlight switch exactly like it is supposed to be wired per whatever switch you have. There are many diagrams for the standard GM headlight switch. Find the picture and hook up info that matches your switch terminals if you don't have a schematic already.
Other than Headlight/lighting:
Fuse panels have direct fuses and they have IGN switched fuses. Example of direct fused components are horn, dome, hazard....
Switched fused component examples are radio, wipers, heater, turn signal, gauges. You may choose a different idea depending on your needs or if you think you will never forget to turn IGN off.
Ign switched components are wired from the fuse panel to their switches, thru the switch to the component. The circuit is completed, thru the component's case and mounting, to intimate contact with chassis ground.
The fuse is protecting the wire, therefore wire sizing is important. Size the wire per amp draw and size fuse per that wire size. Many Google charts for that part.
This is way more info than you asked for. Please don't take it has a lesson to you. You are obviously plenty savvy. Any question about any part? Please ask. I learn by answering and seeing other answers.
Last edited by bartamos; 01/30/2017 8:41 PM.
