I don't believe there is a fuse on the factory or stock 42-7 Clipper dash mounted fog light switch and if following factory instructions, one of the aux fuses on the headlight switch feeding power to the fog light switch is the fuse used for protection.
As far as I know, the factory Clipper fog light switch is a 3 terminal switch and no fuse to work with. Battery in and a separate tail and fog light terminal out is the difference from another switch such as the Electromatic switch which is also an on/off function but with 2 terminals. That switch could be repurposed for fog lights only and could have been used if a true fog light switch was unavailable. It also does not have a fuse and would not have the extra feed terminal to turn on tail lights.
Having said that, it is also conceivable someone could have custom mounted an aftermarket push/pull fog light switch using one of the Clipper dash spots or mounted a Packard fog light switch meant for earlier models separately on a bracket under the dash. In that instance there could be a fuse on the switch and no telling where someone installing the lights might have picked up power.
Many thanks-got both fog lights and backup light working. I think the problem on fog lights was a partial ground-not enough to blow the fuse. It is very difficult to get all terminals on the screw.