Is this link of any value to you? It says 2016 E450 but I am not certain if it's for your vehicle exactly.
https://circuitswiring.com/ford-e-45...e-box-diagram/
Looks like position 5 (relay), 43 (20A fuse) and 54 (10 A fuse for relay coil) are related to the Fuel Pump.....also fuel pump diode assignment near the bottom of the listing.
Maybe someone with your coach can suggest the correct info if this is not correct.
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