As per Steve's comment, see below image from our Monterey. Most coaches of the era are similar. The black box's cover to the right of my legend requires prying off to see the fuses. As with Steve's, the porch light is top right #7.
If the (I think red 10 amp mini - carry spares) fuse isn't blown, it is either the switch or the lamp under the orange cover. If moisture got inside, like any other 12v exterior light fixture, corrosion of bulb and contacts can be an issue. Also be aware that on some coaches the entry lock panel that's to supposedly turn on the porch light by holding down a touchpad is not functional. I guess it was considered an "add on" feature, and Beaver/Monaco did not program in that option, on our Monterey at least.
Joel