I’m about to be running a Walbro 450lph pump in my ‘00 ranger build, and want to run a 10gauge power wire to the pump from my back battery. Seems most logical way would be to intercept original power wire after the connector before the pump lid, send it to ignition terminal of a new relay connected to second battery, send larger gauge power from said new relay to fuel pump; 10-15a fuse on ignition wire, gotta check what amperage I should be looking at for everything, fuse immediately after new relay output to fuel pump, and fuse immediately as wire comes out of fuel hangar lid. Want to be extra precautious since it’s all aftermarket fuel system now. Read the sticky about the fuse not being close enough to the battery and the efan controller melted the truck. Figure same thing could apply to a fuel pump haha. I was just going to run a new wire from fuse box relay but then that bypasses all safeties for the fuel system. I’ll leave this in tact until the truck has suspension work then I imagine I’ll have to bypass the inertia switch to keep it from popping while off-roading. I still have that wire ran through there but will leave it bypassed until I need to eliminate the inertia switch and whatever else is between the engine bay relay and rear connector.

Comments, questions, second opinions? Want to get this engine dropped back in the truck ASAP and fuel system is about the last thing I gotta finish up. Anxious to hear this beast roar! Hope my explanation was coherent enough. Tried to be as thorough as possible

 

If you want to you can, but according to Walbro webpage the 450lph model draws 15amps at 60psi @ 12volts(engine off), and 17amps at 60psi @13.5volt, so OK to power with stock Ranger 20amp fuse/wiring system

One thing for sure, DO NOT exceed the gauge of the fuel pump wires in the tank, any time you run a large gauge wire to a smaller gauge then the smaller gauge will act as a fuse, thats how Fusible Links work, although they are made to separate without starting a fire, the in-tank fuel pump wires will not be that type of wire, lol.

You would use a fused(20amp min) wire to a 30 or 40amp 12volt relay(normal Ford relay) at the 2nd battery, then wire from that relay to an inertia switch, this is optional IF computer activates this relay, if you are using a toggle switch to activate the relay then inertia switch MUST BE INSTALLED; and from inertia switch to fuel pump

Run the relay's coil ground wire from computer pin 80(light blue/orange wire) to relay to activate
Relays 12v coil wire should be key on 12v but doesn't have to be, it only draws .5amp so can be from any Key on circuit.

And don't forget Fuel Pumps Ground wire, if pump draws 17amps then there is 17amps passing thru 12v AND GROUND wires, electricity needs an unrestricted flow, if either + or - is restricted then it will HEAT UP at that restriction.
So if you run a 10gauge 12v wire then you also need a 10gauge Ground wire, again check what gauge fuel pump wires are, that's very important


Alternative idea
The current fuel pump's 12v wire at the fuel pump already runs thru all the safety measures.
So you could use that wire to activate a 2nd relay instead of powering the fuel pump
You would install a new relay with fused power from 2nd battery, and run from there to fuel pump

The new relay's coil would be grounded all the time, then when stock fuel pump relay was activated by computer it would activate the new relay and power fuel pump from 2nd battery
Computer's 2 second cut off would still be in play and if inertia switch tripped it would cut power to new relay so it would shut off power to fuel pump
I would replace current Fuel Pump fuse in engine fuse box with a 5amp fuse, since new relay only needs .5amp.