What gauge wire goes from the starter switch to the battery post on the coil box?
It might already be on the harness, but I have a 1912 engine modified with a starter.
Not sure what harness I put on it five months ago and I am at the office now - don't tell the boss!
Since your car didn't have a battery when it left the factory you won't find any "stock" wire there for the 1912 harness that is available. The entire coil box draws less than 1 amp when the car is running on BATTERY and only 1.3 amps when the car is sitting still with engine not running and one coil buzzing. Thus even 18 Gauge wire would work OK but most folks probably use the same gauge as the timer wires which typically are 14 gauge. A modern cloth covered 14 gauge wire looks to be the same outside diameter as an original 16 gauge wire because the early wiring had much thicker insulation. 14 Gauge modern cloth covered wire looks the most authentic even though it is slightly heavier.