BSWOR you should consider pinning this post.
A REAL Schematic
Until now there were no entire car schematics for our cars, only wire diagrams. This schematic is 5 pages in four separate pdf files (a quirk of my CAD software).
A real schematic rarely makes any attempt to identify wires or plugs or connectors. A real schematic tries to show the internal workings of a component when it helps to explain a circuit. A real schematic simplifies. A real schematic is used when you want to understand how a circuit works.
A real schematic is what the designer makes first, then he converts it to a wire diagram. A wire diagram shows where wires go and how to connect them. You need BOTH to work on a car, unless the wire diagram is just so darn simple you don’t need the schematic.
Our electrical systems consist mostly of switches and lights; around 44 and 41 respectively. Switches are either open or closed. This schematic only shows when a switch is closed. Usually that is indicated by a few simple words below the switch like on, off, run, start, etc. Pay attention to the top section of page one. It shows the most often used symbols on the schematic.
I started this project so I could calculate the electrical loads and know what size alternator to get for my future needs (EFI, fuel pump, halogen lights, power windows, etc.) Amperage information for a stock 1969 Mach1 is in an accompanying spreadsheet (Mustang amps.xls) along with a chart of our most common electrical load: light bulbs. If you don’t like the loads I used to calculate “Likely constant amp draw”, by all means alter the spreadsheet to suit your needs, or use simple math- just don’t complain to me.
My hope is that this schematic and spreadsheet become valuable reference tools for other hobbyists. Edit: I've seen quite a few questions about the 1970 turn signal circuit so I started another topic for "1970 Mustang Exterior lights".