Hola ladies and gents, I have a couple questions that are probably really dumb...but here I am about to ask them. For context, I have a 1983 F-100 XLT LWB 2WD with dual gas tanks and I am trying to consider how I will set up my dual tanks for use with the return style Holley Sniper EFI. It has a regulator built in for those who aren't familiar with it.

I am not sure if I will do this immediately, but I have some spare time and I'm bored. I think long term it would be wise to go with this plan. I intend to travel hauling a Mustang on a trailer, up to 5 hours away. I really don't want to be stranded in another state not able to make it to the track, all because the 13 year old getting paid fifty cents an hour to build a fuel pump in a distant country was having a bad day. With this setup, I could simply switch to the other tank and keep driving. Hopefully the person who built that pump was having a better day and I can get home.

Further context: The Sniper has a fuel pump relay and fuse built into it's wiring harness. It has one blue wire coming out that can feed a fuel pump up to 20A. I want to use that wire, because then the Sniper can prime the pump for 5 seconds, automatically shut it off if the engine dies, etc.. This will keep me from having to wire in a separate fuel cutoff using oil pressure, etc. And I don't particularly want to just have a toggle switch.

(The Sniper does have the ability to run a second fuel pump, BUT that is intended as an aux pump for when the power levels exceed the capability of a single pump. It kicks in at certain RPM or TPS levels (don't recall which offhand). Won't work cleanly for dual tanks I don't think.)

OK, so the part I really need help with: I am trying to decipher these pinouts on this fuel tank selector valve. Part number FV5 from Standard Motor Products.




I used to think I was decent at doing that. I spent two years studying automotive in high school and another two studying engineering in college. I would think I could figure this out. But this manufacturer has the weirdest wiring diagram for this tank selector I have ever seen. Or maybe it's just late and my brain isn't firing on all cylinders. It doesn't really help that this style tank selector is set up to do a whole lot more than the one in my 83, which currently uses 1 wire.

ALL I want to have the selector switch do is flip the supply and return lines back and forth at the same time. I don't want to accidentally pull fuel from the front tank and then return it to the full rear tank and overflow it. I do NOT want to have the fuel tanks OR sending units wired into it. I want to leave those in their factory locations and NOT slice the wiring harness up inside the dash. It's all original right now (except the radio).

Essentially, I want the single wire that currently goes to the selector valve to operate two single pole double throw (SPDT) relays.

When the factory tank switch is set to the aft tank, the coils on the relays should not be energized.
The aft fuel pump will be wired to the normally closed 87A pin.
The tank selector valve will be in it's normal position, pulling fuel from the aft tank and also returning to the aft tank.

When the factory tank switch is moved to the auxilliary tank, the coils on the relays are energized.
The aux fuel pump is then getting power from the normally open 87 pin.
The tank selector valve actuates to pick up the fuel AND return it to the aux tank.

That can be seen (hopefully) on the rough wiring diagram I made below...obviously it isn't finished, since I don't know which wire off the selector valve to use. You can see the spot I am questioning inside the big red circle with the question marks. Also, it's been too long for me to remember the symbols for everything lol. So hopefully it's understandable enough. It makes sense to me...but of course it would, I knew what I was thinking when I made it.



If that photo is fuzzy, here's a link with it in PDF form so you can zoom in better quality: https://drive.google.com/file/d/1H95...ew?usp=sharing

Aside from the question and problem above, does anyone see any glaring issues with my plan here? I don't know too much about this circuit. I am going off the 1985 year model wiring diagrams, also, but I would assume the 1985 and 1983 have fairly similar setups in regards to the Fuel Tank Selector Switch wiring?

Thanks in advance, yall!

 

Ok. You need to use that 6 port valve obviously for your fuel lines. One thing you have to consider, this valve has a little dc motor in it. It runs a spool in the valve back and forth. You are going to need something a little more complex to run that valve. It needs to be wired like a electric window. The polarity has to be swapped to the two motor wires on the valve for the valve to operate. That is what that toggle switch with the criss-cross "X" to it is doing in the factory valve diagram. It swaps the polarity on the valve on terminals E and D making the valve switch.

 

Here's a idea I came up with and the diagram for it. Any way you do it, you are going to have to coordinate everything together. In other words when you plumb the valve in, and it's in certain position, you will have to make sure the correct pump is being activated.

 

OK! That's the missing link here! I did not know that the polarity switched back and forth. I thought it had a "normal" resting position and when it was powered up, it switched to it's alternate position, which is how the stock one works I believe. That helps me, as does your diagram. Back to the drawing board.

 

Dave, do you mind checking me out here?

If I understand this correctly, I just need to switch from positive to negative on the E and D terminal. That's what someone said in a reply on the Bullnose Forum. But I wasn't comprehending what they were saying till I read your reply.

Here's the new wiring diagram with a DPDT relay to switch the polarity back and forth: https://drive.google.com/file/d/1BUB...ew?usp=sharing

 

I think it will work. I am trying to get a movie going in my head as to how you would hook everything up and get it right.

Obviously your dash switch is labeled front and rear, so that is set in stone. So I guess you could wire the relays up, set the switch to front, and then touch the front pump to one relay terminal and then the other to see which one makes it run. You have your diagram showing the original valve wire is hot when it's on the rear tank? Is that correct? Doesn't really matter if you just touch the pump wire to the correct terminal.

The tricky part will be the valve. I am guessing you could use air from a air compressor nozzle? With the dash switch still in "front" try to blow air through the valve, and see which set of lines is connected to the main lines that go to the engine. Then hook the front pump to those lines?

 

I pulled the info for the dash selector wiring directly from this diagram: Wiring Diagrams - Gary's Garagemahal (the Bullnose bible)

It shows that when the dash selector is on the front tank, the solenoid is not normally receiving any power. When it switches to the rear tank is where the positive 2 volts comes from the power distribution panel. I can test that with a simple test light any day...just put it on front tank and make sure no power to the single wire on the stock valve, switch to rear and make sure I have 12v at the stock valve. I feel pretty good about that part though.

I also feel really good about the pump setup switching. That only depends on having 12v when the switch is moved to the rear tank.

I figured I would test the valve to make sure I get the polarity right prior to fully installing by hooking up the front fuel pump and then putting some test return lines into containers. Power up the front tank, make sure that A.) the front tank fuel is making it through the switching valve, and B.) that it is returning from the correct line. All I need to test the setup is the return lines unhooked and a new line off of each return port on the valve going into a container marked "front" and another marked "rear". If they come out backwards, I simply swap the polarity at the valve (move the line connected to "E" to "D", and vice versa).

That sound like a plan?

 

Sounds like you will be able to get it figured out. Looks like Amazon has some 12vdc dpdt relays with sockets also. All that stuff needs to be sealed from the weather. That would be a lot of wires leading from under the hood to the frame rail area if you use the stock switching valve location Ford did. I guess you could keep it under the hood if you ran the 4 fuel lines all the way up front. Or you could possibly get a sealed grey PVC box from Lowe's, mount the relays in it, and mount it under the truck on the frame rail.

 

Sealed box is exactly what I was thinking. I work in industrial automation, and we stock them, so I can just grab a watertight NEMA 4X rated box and throw them in there for safe keeping.

I don't want it under the hood; part of the plan while this is all getting done is to clean up the engine bay and wiring.

Thanks for your help, Dave. I'll let you know how it goes.

 

I am going to be making two minor changes to this circuit. I haven't yet found a DPDT relay made for automotive. And the industrial ones I have here at work are too big to fit in a box cleanly/easily without going to a pretty deep box. They're made for mounting on DIN Rail. So I am going to use two SPDT relays instead.

However, this presents an interesting issue that I did not notice the first time and would actually probably be a non-issue with a proper DPDT relay. If you look at my most recent wiring diagram with the DPDT relay, you will notice that there could possibly be a circumstance where, IF one contact made, and the other did not, there would be a short.

Thankfully, I think the solution is simple. Turn the relay around and have the E & D terminals on the commons (30 pin). This way, even if one of the contacts didn't close, it would simply be GND to GND or 12V to 12V. The only possible way the 12V and GND could ever come into contact is through the load...which might be an annoyance if I am trying to switch the tanks because one is empty, but certainly not going to burn up wires or pop fuses or anything.


This is the circuit under normal, unpowered conditions. No issues there. If BOTH contacts make at the same time, no worries, life is good.


This is the circuit if only one contact makes. This is if the contact was stuck in it’s NC position…maybe a wire to just one of the relay’s coil were to come undone or the relay gets old and can no longer hold the contacts. Whatever the case may be. As you can see, there would be a short from positive to negative. I planned to fuse that wire anyway, but I’d rather avoid popping it.


This is the new circuit under normal, unpowered conditions. No issues there now. I am still reversing the polarity of the switch, just doing it in a different place.


As you can see, even IF only one relay makes contact, the 12v and GND are isolated to only contact themselves.

 

Would this one fit?

 

I saw that one and thought it would work, but the pins looked fairly small and I was concerned about them staying connected. Looking at the dimensions, though, it might just be that the relay is bigger than I thought and maybe the pins are the same size is others. I might give that a try. It's only $10 to try it out I guess.

I was going to roll with these:

 

The double relays would work also. Whatever you think is best for your situation. Like you said, a fuse should protect it if one of the relays got stuck or didn't switch correctly. The valve will stay in it's last position if something bad happened. So I would make sure I switched the tanks over little below 1/4 full, and not go till you were really empty. That would give you some leeway to find somewhere to fill up the only tank you had till you got time to fix it.

 

P.S. Did you mention you worked in a industrial environment? I was wondering if you have ever seen the 3 phase reversing contactor pairs for 3 phase motors? These are just two big relays or they call them contactors, and they can have that sticking and dead short failure mode also. But they are specially made with a mechanical interlock between them, only one can be activated at a time, and if one sticks, it mechanically will not let the other one activate. Large 3 phase power being shorted line to line, makes a big boom, been there done that.

 

It probably would be smart to switch early just in case...I got screwed by that in high school when I first owned the truck. A parking lot is no place to find out your tank selector valve doesn't work and the kicker was, I thought the sending unit was just bad, so I refilled the tank that didn't work once again.

As far as reversing contactors go, I build one using two Allen Bradley 100-C30D10 contactors and a 100-MCA02 mechanical interlock once a week lol. That, along with a 105-PW37 power wiring kit, makes a 104-C30D20 reversing contactor.

We don't stock anything over 23A in reversing flavor, and usually our customers need a 30A or greater. Thankfully we keep all the parts in stock to build one. Typically, if they're asking for one, they don't have time to wait to order one. Contactors don't exactly get routine maintenance.

I'm kidding bout it being once a week, but I do it often enough I know the parts off the top of my head, sooo...however often that is