Ok, so you are losing almost 2 volts between the battery and the ballast. Might be the ignition switch, or the bulkhead connections. Can you measure the voltage at the battery side of the ignition switch connector?

If it's close to 13.6, put the switch in run and measure the output of the switch.
If the input to the switch is close to 11.8 instead it's time to clean you bulkhead connector.