Dome lights won't go out

Has anybody with one of these vans expereinced this before? A friend has this that he uses for work and I know he has two doors, a side door and a rear door that all have the light switches. The switches all seem to be in working order.

Any ideas? Dimmer switch wasn't locked on. Could these be the problem? Thanks

You didnt list the age or model of the van, but that notwithstanding,.many domelight switches operate by grounding the light... thats why they are able to get away with those tiny switches. Some simply complete the circuit internally. regardless, sometimes they get wet or contaminated and that negates their normal function, turning the lights on continuously in some cases. look at the one on the door that has the poorest-condition weatherstripping and check it out first... just take off the door or kick panel, and unthread the nut from the switch in the jam to allow pulling the switch out for inspection.