I do not know the chassis but I do know Workhorse. And GM in general.
On a workhorse front and center.. open the hood and if like me you are six foot. Directly in front (Center) is a black plastic box.. It's in there
On my 1992 Lumina the relays were on the top front rail (Radiator mount rail) passanger side. and it's one of them.
Generally relays are all "Grouped"
Never had a fuel pump relay fail
Did have the starter pilot relay fail (Yup right next door) fixed it (Actually fixed the relay... .Yup I know how to do that).
Horn relay is there too.
HEVAC blower.. Same spot.
