When you add a external electric pump will it suck gas through it even though the in tank pump has gone out ?
My aux pump on the side rail would not suck the fuel thtu the intank pump unless the intank pump is running. Wire them both in parallel.
If the in tank pump fails seems to me your still screwed because the external pump wont work if the intank pump fails.. In other words the external pump cant get the gas if the intank pump is dead. However if the intank pump is just weak then thats a different story. As long as the pump is working even a little the external will probably work, but if it is kaput your out of luck..