relay engine?

t reg dispatch van i bought had wrong engine fitted managed to track down an engine 1.9 diesil from a citrion relay van was told it was a straight swap now that ive fitted engine ive came accrosss a problem with the wiring for the fuel pump.the relay one has 3 wires on it and the one for the dispatch has 4 wires .the dispatch one has 2 lives 2 earths as i said brfore the relay one has only 3 does any body know what the live feed is on the relay one