Fuel Pump wire harness

I had a back yard mechnic trying to install a used fuel pump in my baby and he says he's stumped because the pump has a 4 wire output but the wire harness is only 3. I talked to Dodge and they saidl, it's correct and how it's supposed to be evidently 2 wires are grounds-the extra for the sensor or something. Anyhow he's got the gas tank reinstalled and the used pump is working- but has low pressure and won't keep the van idling. Could this be the wiring is not correct, bad pump or any other ideas? The filter is supposedly fine.

If the pump is working, the van will idle properly. If not it will idle poorly.
You can test this by disconnecting the connection right by the fuel pump. I have done this before. When I replaced the fuel pump I forgot to reconnect the electrical line. The van started but idled poorly. I reconnected the electrical line back and no more idling problems.