The power wire into the pump relay is labeled 1126, the power wire from relay to pump is 1041, both are 12ga white.
I believe you indicate there is 12v to the coil of the relay but no 12v to the power side, i.e. 1126.
You don't state if you have checked continuity between 1126 and 1041 to verify the relay is working.
Paper schematics I have indicate 1126 is fed as follows:
Chassis disconnect switch, if original setup, shows 2ea #2red inputs into switch (from chassis batts & from chassis/house isolator, and then single #2 out to a pair of 105A self-resetting breakers or fuses (don't know physical location). At the pair of 105A overcurrent devices, 2 studs @ each device 4 studs total you will find:
First device: 1ea single stud has 1/0-red out to front firewall main positive stud
The opposite stud on that device has 3 wires, #2red in from chassis disconnect, unknown sized red that hops between this device & the other 105A overcurrent device, and 1ea #6red out to one of the grid heaters for engine intake air when it is cold.
On second 105A overcurrent device, one stud has two wires, and the other stud has one #6 unknown color, probably white & labeled 1126, out to pin R of a 9-pin "engine/chassis" connector (can't tell you where, sorry). From the opposite side of the 9-pin connector, #6 1126 has a splice in it to #12 and goes to the relay in question.
If the 105A fuse burned (or if its a breaker that has broken) then the 1126 wire has no 12V. If 105A fuse is intact w/voltage on both sides, then open condition is elsewhere in the circuit.
Baja-tested '08 2-slide 36'
Alpine: The Ultimate DIY'er Project