there really easy to wire up to a switch as long as its not the cheapos that have the transformer bit in the ciggy lighter bit...
There not illegal on the inside as long as they are below the window level and dont dazzle other drivers, the police dont bother with mine, i have 4 blue ones, and blue tints, so they are really noticable...
best to keep em on a switch though just in case they are lookin for somethin to do you for, at least you can switch em off !!