When you need to test a John Deere fuel pump, the first thing you'll want to do is make sure that the fuel system is completely empty. Next, disconnect the negative battery cable and remove the pump from its housing. Once the pump is removed, connect it to a 12-volt power source and turn on the ignition switch. The pump should now be running and you can check for leaks. If there are no leaks, then your John Deere fuel pump is working properly.