I wanted to clarify a point about Model T wiring I previously made here to avoid any confusion.
The reproduction wiring looms sold today SHOULD (some do not) use #12 gauge wires for all the charging charging circuit wiring and DO use #14 gauge wire for all other wires.
To be absolutely correct per the Ford wiring loom prints, which I have in my files, all charging circuit wiring SHOULD be #12 gauge wire and all other wires should be #16 gauge wire.
As I indicated in the past there are several Model T wiring diagrams floating around out there and many are incorrect in one way or the other.
Here for your future reference is a wiring diagram that shows all factory wiring correctly depicted (including the commonly incorrectly depicted physical wiring of the charging circuit to the ammeter via the switch)and I have added a note indicating the proper gauges of all wiring.
If you have a stoplight installed the hot wire should be wired to terminal block connection #1.
If you have the commonly recommended 25 amp main fuse that will protect all the wiring it should be installed in the wire from terminal block connection #3 to point G as close as possible to point G.
I particularly like this diagram because it has each location uniquely marked and is easy to use when helping people with wiring difficulties over the telephone.
I hope this helps clarify this commonly misunderstood subject.
Ron the Coilman
Would there be any issue using #12 for everything excluding the heary batt lines?
They don't fit well through the channel under the steering column if you have a car with the combo light/horn switch.