11.3V tells me the charging system, isn't.

When it's running 13.8V is more like what you should see. It will vary a bit, but should be in that ballpark. Low voltage tot eh ballast means low voltage out adn low voltage at the coil.

Fix that first, then see what's at the coil. If this is a dual ballast resistor you probably have it hooked up to the wrong side, 2.5 Ohms is way too much.

How voltage drop works is simple to figure. Measure from the ballast input to ground (no voltage applied). Subtract the ballast resistance, in this case 2.5 ohms. The difference is the coil resistance. Let's say both are 2.5 ohms, then the voltage at the coil + will be half the voltage at the input to the ballast, the equally drop the same voltage. If the coil resistance was 1.25 ohms and the ballast is 2.5 then the ballast would drop 2/3 of the voltage and the coil the remaining third, so at 12V into the ballast you would see 4 volts at the coil +. IOW, the percentage of resistance the coil has in the circuit is the same percentage of voltage dropped across the coil.