Mannyrock, 3 #18s to carry the hot to track should not give greater voltage drop and 1 #14. You will find voltage drop through the track. Do make sure your ground (neutral for the AC purists) is of equal ampacity, and have frequent drops to the track. There is voltage drop on the ground circuit & outside rails just as on the hot.
While the bottom of the line HF multimeters are not of Fluke accuracy, they are good enough for train work and no great loss when dropped on concrete or into the river
