There will be 12 volts going to the 24 volt load when the switch is in the 12 volt position but since the headlamps are in series with the circuit, if the bow thruster were turned on, only a couple of amps would flow and the headlamps would light.
(only a couple of amps; would flow; ) (12 volts; going; to the 24 volt load) (the headlamps; would light; ) (the switch; is; in the 12 volt position) (the headlamps; are; in series with the circuit) (the bow thruster; were turned on; )
only a couple of amps 12 volts the headlamps the switch the headlamps the bow thruster
would flow going would light is are were turned on
to the 24 volt load
in the 12 volt position
in series with the circuit