Hi RichB,
Best thing to do is look at a wiring diagram to figure out what's going on with the light; then we can track down likely places that could be a problem; in most cases the light always has power and gets turned on by providing a ground, so a bare wire shorting on the frame anywhere can turn the light on.
However, we'll need to know the year and any submodel information that's relevant to be able to find the right wiring diagram. Please update your question and we'll be able to proceed.