Look near the oil filter and see if you have a fuel pump on the side of the engine block.
If you do you do not have a relay.
If you do not have the fuel pump on the side of the engine then there should be two relays for the fuel under the hood.
I would guess that your Ford E350 cutaway RV chassis is a 1986 and may have the engine pump. Most E350 cutaway RV chassis are one year older than the home title says. Check the VIN number as the number (letter) in the tenth position will tell you what year it is so you can get the right parts for it.
1987 should be an "H" and 1986 should be an "G".