Well would the fact that the connection to the pump gets the proper voltage in forward or reverse rule that out? I mean that fact alone says its a pump issue but I have the same problem with old and new pumps (and they work fine on a car battery) and THAT says its a boat issue. A lot of finger pointing but no smoking gun.
We did consider that the switches at the helm were having issues (do they have relays?) but the fact that the connection get the proper voltage in both directions caused us not to take apart the helm to check out the switches.
(I mean "us" as in me and my neighbor as now I have him sucked into this problem as well.)