Voltage drop at ballast resistor
The voltage is 10.45 at the blue wire while 12.45 at the battery.
Well, if it was me, I'd check the bulkhead next, and then whatever is easier working back to the battery -
It sounds like you are testing with engine off - ignition on so power is from battery. So using my '67 as an example, I'd check N, P, and Z.
Understanding Charging Systems with Ammeter
Of course the cavities on your '72 will be different. Because these are easier to access, I would (and have) started there. Using those readings, decide where to look next. For example, if N and P both read 10.5 Volts and Z read 12.5 Volts, then the problem isn't at the ignition switch. Therefore it must be from main splice to ammeter to bulkhead inside at Z.
But, if N had read 10.5 and P was 12.4, then the wires to start switch, or the bulkhead connection at N must be where there is poor connections or shorting.
