Be careful, the real problem is if the pumps have waited a decade or so on a shelf for a new life in your pride and joy's engine bay, the inner switch gasket (not replacable) has probably dried (small cracks in it), meaning it is f..cked up.
The pump will then run dry (or with some carb cleaner as well) correctly, but with some fuel, you could have leaks from the pump body to inside of the switch, where are the electrical contacts, opened and closed by the "actuator pin" (don't know its correct name in English).
Not something you want to experiment... only a good idea during winter, if you're feeling cold in your workshop :drunk:
I've 3 pumps, running perfect dry, but I only trust one switch, which is like new cause it has been lightly used and, above all, continuously since it was made (i.e. the gasket have never dried...)