Title says all.
For your 1916 touring there is a single wire that goes from the light switch to the magneto post on the coil box. The wire runs above the first three of the four lower coil box posts. If you are a purist, the wire is attached to the firewall by two staples that have paper insulation (bell wire staples).
The wire is the same type and gauge of black cloth covered wire that is used for the horn button wire and the wires at the headlights.
Additional comments:
Lang's used to sell a wiring "kit" that had enough wire to do both the horn button and the headlights for the pre-starter cars, including the short length between the light switch and coil box magneto box described above.
I found the horn button kit online as well as the correct wire sold by the foot:
http://www.modeltford.com/item/5042H.aspx
http://www.modeltford.com/item/5042W.aspx
I just sent Erik a P.M.
I responded with a pm including pictures and a Ford issued wiring diagram. I've also posted below.
The lights are wired in a series.
The light wire that is part of the loom is attached to one of the terminals on the light switch. At the front of the car, the light wire exits from the loom, prior to the four timer wires. This wire is attached to one of the terminals of the passenger-side headlight. A second wire runs from the passenger-side headlight and through a tube in the back of the radiator and to the driver-side headlight. A second wire runs from the driver-side headlight and is grounded to the radiator stud.
Below is the wiring diagram from the Ford Manual and five pictures of the wiring on my dad's 1917 touring. It does not have the two bell wire staples described in my prior post (the staples are something that we recently discovered should be there based on the original dashboard of my unrestored 1917 roadster and photos of the 1917 "Rip Van Winkle" touring). The wiring is the same for your 1916.
The clip that holds the loom on the dashboard of my dad's car is the same location as the 1917 Rip Van Winkle touring. The clip on my unrestored 1917 roadster is in a different location, to the left of the carb rod and even with the light switch. All three are Minneapolis assembled cars, mine is May 1917, Rip Van Winkle June of 1917 and my dad's car July of 1917.
Thank you for the pics!
To answer the specific question, in the T era electric splices were wrapped in a layer of rubber tape, then a layer of friction tape, which is cotton tape impregnated with a rubber-based adhesive. I watched my dad do this many times when working on house wiring. In fact, I'm so old that I've done it myself before modern plastic tape came along. In cars, another type of splice was a bakelite tube containing a brass conductor and the two wires with bullet connectors shoved into the ends.