Location of the Boost Solenoid
See the diagram below. It shows the "Front Distribution Panel," which is in a box in the compartment directly under the driver's left foot, accessible from the outside (that is, the forward-most compartment).
The charging solenoid ("boost") is in red. I believe the "continuous duty" and "boost" solenoids are two terms for the same solenoid. This solenoid connects the chassis and house batteries while the engine is running, so the engine's alternator can charge both battery banks.
The other solenoid, shown in blue, is used to cut off some DC loads from the house batteries. It is activated by the almost legendary "salesman switch" near the front door.
2008 Holiday Rambler Admiral 30PDD (Ford F53 chassis)
2009 Honda Fit Sport