Every day when being used, whether or not there are other passengers. Boats should have minimal Coast Guard required equipment on board (life vests, fire extinguishers, ropes, etc).
If the fuse is working, then check the bulbs.
Check fuse box. Your operator manual should show all fuses, their location, and what they protect.
Check the operator's manual, if you have one. It should tell you in there.
check they have water
The operator
Check your warranty
the coolant level
After you have been working in the engine compartment.
To determine if an operator is Hermitian, one must check if the operator is equal to its own conjugate transpose. This means that the operator's adjoint is equal to the operator itself. If this condition is met, then the operator is Hermitian.
check the fuse.
They should check the solid waste from the person
Check to see if parking and tailights are working - should be the same circuit - check fuses May be the dimmer rheostat needs replacement