I was going to say earlier that the OEM circuit for an in tank pump has a bunch of interlocks, like initial run to pressurize, safety interlocks, oil pressure interlocks, etc, etc and they are all but silent when running due to being submerged, which is by design. Trying to draw through the stock pump with the suction of another pump, either mechanical or electric is a bad idea. I expect you've still got a power source to the stock pump, and you need to either use it or drop the tank and remove it, replacing it with a proper suction line.