[B_man_Al]

Below are some results I measured on my 8BA with a 6V coil, and a nominal 1 ohm ballast resistor. It has been converted to 12V.

I found the best way to estimate the primary current was by adding another small series resistor ( 0.18 ohms) between the coil and ballast resistor. Or measure the current directly.

Here are the measurements, and the resulting calculated currents and resistances:

Meas Battery V : 11.87V (engine not running, points closed)
Meas V current sense resistor: 0 .752V
Meas V coil (cold) : 4.95V
Meas V ballast resistor (cold): 5.90V

Adding all these gives 11.60V vs 11.87V measured across all of them.

Calculated coil / ballast resistor current = V sense/R sense=.752V/.18 ohms= 4.2A

Calc coil resistance = V coil/I coil = 4.95/4.2A= 1.2 ohms
Calc ballast resistance = V bal/I coil = 5.9/4.2A= 1.4 ohms

The ballast resistor is marked as 1 ohm, so it seems a little high.

As it warms up over time, the current drops to 3.5A and calculates out to 2.2 ohms.

Hope this helps
Al