Fuel Pump not priming

I have a '99 Sport Nautique with the GT40 engine. My fuel pump does not always prime when I turn the key (which means the engine won't turn over due to no fuel). I found that if I "fiddle" with the fuel pump sending unit (not sure exactly what it is called, but is a small black "box" mounted on the rear portion of the engine by the fuses) the pump will prime. Does lead to a bad unit, or simply some loose wires or dirty connections?

thanks,
Kent

If that small black box is a fuel pump relay, then it should be easy and cheap to replace. Also check for loose or dirty wires at that connection.