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Seeking clarity on Dual Tanks and Fuel Gauge

conor_nolen

New Member
Joined
Jul 25, 2017
Messages
26
Loc.
San Francisco
I am a new Ford Bronco owner (1974) and trying to figure out how to manage dual tanks and gauge the level of each tank accurately. I have a fuel tank switch below the driver seat and it appears to operate effectively but does not impact the level of the gauge when switching between tanks.

Questions:
1. Should I use rear as my go to tank and lean on aux front as a back up only when needed? Or should I use them both equally?
2. Should my fuel gauge be reading the collective level between both or Change based on the tank I have selected?
3. Is it worth while to upgrade to a single, larger rear tank and remove the dual tank setup altogether?

Thanks!
 
Last edited:

okie4570

Contributor
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Jul 16, 2012
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NW OK
It's pretty much personal preference imo. Do you not have a tank switch on the dash, left of the steering wheel? The valve under/below the seat only switches the tanks, where as the switch on the dash affects your fuel gauge on the cluster.
 

okie4570

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Jul 16, 2012
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Yes usually on the far left edge of the dash. It may be bottom or center depending on whether handle throttle was present, etc. Do you have two sets of sending wires (one from each tank) going up to the dash or one?
 
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conor_nolen

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Joined
Jul 25, 2017
Messages
26
Loc.
San Francisco
I do have a small switch on the bottom left side of dash but it controls the supplemental Hella lights that the previous owner mounted on the front bumper. Is there a trick to identifying "sending wires"? Perhaps they were disconnected at some point.
 

blubuckaroo

Grease Monkey
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Jun 11, 2007
Messages
11,795
Loc.
Ridgefield WA
Questions:
1. Should I use rear as my go to tank and lean on aux front as a back up only when needed? Or should I use them both equally?

Yes, the rear is the main tank. However, you really should use all the fuel in the aux tank from time to time. Especially with the ethanol fuel we're getting.

2. Should my fuel gauge be reading the collective level between both or Change based on the tank I have selected?

If your car came with an aux tank from the factory, you'll have a switch on the dash to select which tank the gauge is looking at.

3. Is it worth while to upgrade to a single, larger rear tank and remove the dual tank setup altogether?

Certainly that's your choice. If your car won't be getting far from a gas station, then a single tank is fine. I use our car for hunting so I've replaced both tanks with the larger Aero replacements. I'm planning on adding Aero's passenger side tank too.
 

Steve83

Bronco Guru
Joined
Jul 16, 2003
Messages
8,980
Loc.
Memphis, TN, USA, Earth, Milky Way
1. Alternate them so there's always reasonably-fresh gas in both. When one gets low, switch, and fill the low one.
2. Only the selected tank.
3. No. There would never be any return on that money.

This diagram shows how the fuel gauge was wired originally:



Click it from a computer with a monitor (not a tiny phone screen) and read the caption.
 

Broncobowsher

Total hack
Joined
Jun 4, 2002
Messages
34,833
Left of the speedometer is where the gauge switch should be at. They go bad and are often removed and just one tank is hooked up directly to the gauge which may be what happened to you.

You can run it any way you like. But you should use the fuel from both tanks. Don't keep one as emergency fuel. The gas will go bad and won't be usable. Make it work as you feel it should.

A lot of us have ditched the two tiny tanks and gone to a single large tank. It does simplify life. No having to switch tanks, trying to remember "did I already empty that other tank"? Only those who go great distances will find the need for extra fuel over what a 23 gallon tank offers.
 
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conor_nolen

New Member
Joined
Jul 25, 2017
Messages
26
Loc.
San Francisco
I took a few photos and shared them here. https://www.icloud.com/sharedalbum/#B115GH8MqHhlQe

I took one of the wires coming out of aux tank (looks like only a ground is there) and also a pic of the dash showing the switch (which cottons my Hella lights now).

I also include three other photos showing items in the engine compartment. I have no idea what these items are (first two) and the third is strange. Looks like a tube that should be connected but instead has been capped on one end and a screw has been put in the other end haha. Not sure at all what's going on here and was hoping he Bronco brain trust could help. Thanks!!!
 

Steve83

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Jul 16, 2003
Messages
8,980
Loc.
Memphis, TN, USA, Earth, Milky Way
In the first photo, the Orange wire is clearly cut.

The Hella switch is in the original fuel tank switch location.

The "HEAVY DUTY" object is the ignition module. The gold one is the voltage regulator. No telling what the relay beside it is for - maybe the lights. The taped Yellow wire nut is not good.

The vacuum line with a screw is probably from the SPARK port on the carb, for the distributor vacuum advance, which is capped beside the valve cover. The "Prestone" cap is on a loop that bypasses the heater core, so it's only good for bleeding air out of the coolant system. There's no fan clutch. The PS pump is a Saginaw, which is good.

The more pics you post, the more we can help you ID parts & problems.
 

okie4570

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After looking at your pics, I'm thinking the previous owners were doing the "fill both tanks, run the front till she sputters and then switch tanks" method lol.
 

jckkys

Bronco Guru
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Mar 15, 2012
Messages
5,196
The PO was obviously a fan of Rube Goldberg repairs and modifications. The entire engine compartment wiring scheme has nothing to do with the OE harness. He put a garden hose male in a heater delete loop. Why? Who knows? With all my EBs 2 of which were new, I filled whatever tank was empty and ran on the other till it was empty and filled that one. This way I never had stale gas in either tank. I got good at reaching down and switching tanks when the engine began to loose power. Then of course I switched the fuel gauges. This routine worked well for many years. The stock tanks allowed me do drive further than any car I've owned and they're out of harm's way. Jerry cans at the hunting camp are an additional backup. They're needed for the generator anyway.
 

DirtDonk

Contributor
Bronco Guru
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Nov 3, 2003
Messages
47,345
Can you post some more pics of the complete dash? Looks like it might have been changed. Certainly some of the switches have been.
Heater hose has been looped because it looks like the heater core was removed.
Factory smog stuff was removed, including the "Thermactor" air pump and probably many vacuum devices, including the vacuum connection to the distributor as was noted.
No telling what the two different relays control. As said, the lights are probably one of them, but hard to say what the other is.
It's possible that the truck didn't come with dual tanks from the factory and the second one was just added later. But since the dash looks changed too, it's hard to say. Easy to add one later.

As Steve was asking, more pics of the engine compartment might enlighten us a bit more.

Looks like you have some tracking down of things yet to do on your new Bronco.

Good luck.

Paul
 
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conor_nolen

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Joined
Jul 25, 2017
Messages
26
Loc.
San Francisco
@BluBuckaroo The Fan/radiator thing you were refenceing is some sort of transmission cooling system because the stock vents above the wheel well were capped bc the previous owner used to take the Bronco through the river and wanted to reduce water in the engine.

@steve83...thanks for the information! Super helpful. I am thinking of going whole hog and replacing both SENDING units, new switch with the electrical conversion for the tank selector. Thoughts? Seems like a good investment but wondering if that work requires someone wise in the ways of this effort or if I could DIY the project. As for the "taped nut"...there are a number of places where this type of "home style" harness is being used. Assume it's best to redo these with the proper wire harnesses? Any suggestions there? I'll take a few photos shortly of the lines that have been capped and private message you once I have them up.

This forum is seriously heaven sent. Learning so much! Thanks ya'll!!
 

blubuckaroo

Grease Monkey
Joined
Jun 11, 2007
Messages
11,795
Loc.
Ridgefield WA
@BluBuckaroo The Fan/radiator thing you were refenceing is some sort of transmission cooling system because the stock vents above the wheel well were capped bc the previous owner used to take the Bronco through the river and wanted to reduce water in the engine.

It looked sort of like an added tranny cooler. How efficient could that possibly be in a hot engine compartment? It needs cool outside air.
 
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conor_nolen

New Member
Joined
Jul 25, 2017
Messages
26
Loc.
San Francisco
Not sure what kind of difference it makes but I just drove 3.5 hrs straight from bay to Tahoe averaging 65 mph and tranny temp stayed around 180-190 degrees. Not sure if that is high or not but was happy with how she drove on her first trip to the mountains.
 
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