He is using an analog meter, maybe reading off the wrong scale?
My suggestion would be to buy a half-way decent digital meter and see what voltage you have at the pump when depressing the prime button. With adequate voltage the pump should sound about the same as when you powered it straight from the battery. If it is about the same and you have no fuel from the line, there is probably a bad fuel line to the pump from the source. If it doesn't sound the same, you may have a bad electrical connection to the pump.
Good luck, I hope it's an easy fix.