I am not planning on using two fuel guages, but wondered if it could be done.
Can the instrument cluster and tank sender wiring be modified so that fuel levels from both tanks could be simultaneously displayed from the cluster?
The tanks would still be controlled by the dash switch, but each sender would always be hot and reading the level. On my 92 150, I would remove the voltmeter on the right side/top corner of my cluster display and put a new fuel gauge in its place. The gauges could be labeled "front and rear"
I think it is a cool project.

 

I had just wrote my interest of doing this exact thing, I hope you get some great feed back on this. I think it could be done, but have no idea really. I am pulling my bed off and the wire that operates the fuel gauge will go to sunpro gauges, two of them. I have ran out of fuel too many times while having a full tank in the other tank.
This would surely be a great look to the gauges I have already installed.

 

Very cool project, and maybe what I'm doing with my truck might help you.

I found that on my 93 F350, both fuel senders are connected to the switch in the dash, so I simply removed those wires and attached them to an DPDT relay, and using a simple circuit the relay closes for 5 seconds, then opens for 5 seconds, then closes for 5 seconds, then opens for 5 seconds. My factory cluster can go from full tank to empty in about 2 seconds, so my fuel gauge moves back and forth indicating the two tanks.

The only thing I didn't do is have any indication as to which tank is displayed. I was thinking about putting in two small LED's into the fuel gauge, the left one being the front tank, and teh right one being the back tank, but I've never gotten around to it, so I just have a pulsating fuel gauge if the tanks have different fuel in them. I didn't bother finishing this beacuse the factory cluster is leaving soon anyway. I'm almost done making a new dashboard and fitted into that will be a digital t-bird cluster. I'll be using the fuel gauge of the t-bird cluster to indicate boost (turbocharged big-block) and on the touchscreen next to the cluster, behind the shifter, I'll have an "X" application that displays fuel from both tanks. I started breadboarding a simple A/D to "flash read" the two tanks, and provide a value 0-15 for each tank, pack them into a byte, and send to the parallel port of the computer that drives the touchscreen. I haven't finished as I have too many distractions, but it's sorta working on the workbench. The computer can read the fuel levels, and display "stuff", I just have the scaling way off. I don't recall if it's because my scaling in the software is off, or if the junkyard floats I have are not right... it's been a while since I've monkeyed with it.

 

Forgive my ignorance in not seeing the purpose of this. I check my fuel levels when I first start the truck up for the day. As far as a trip, usually both tanks are filled, when one is low or going on empty, you switch. If the system is operating properly, you'll know exactly how much fuel you have by switching tanks. There is no interruption of operation when doing this and only takes about 2-3 seconds for the guage to read it's capacity. The only benefit of knowing what both tanks read simultaneously is if you are running both tanks at the same time. On models with the DFR, this is impossible since it requires fuel pressure from one of the tanks to open the valve for that tank to allow flow to the engine and return fuel. I'm not sure about the FDM but they function about the same as they require fuel pressure to open the return valve. They may be wired to run constantly so both tanks can feed the engine but I don't know how the return would work, it may default to the front tank being it's the closest to the engine. If this is the case, then you would have one pump constantly running on empty and this would definately damage that pump as you would no longer be able to turn it off.

 

I am not that bright when it comes to the operation of the fuel delivery on the duel tank truck. I ran out of gas while having a full tank in the rear because I just bought the truck in early May and filled the front tank and then rounded the cash amount off with the rear tank with it being almost full.
I had put some expensive injector cleaner in the front tank and wanted to run it close to the bottom to get the full effect of the cleaner and ran out of fuel while the tank read a little more than 1/4 of a tank.
I had switched tanks when they were both full and the hand moved down and the engine had kept running so I thought that part of the system was fine, I go back to the front tank and ran it until it quit as mentioned above.
I figured no problem, I have electric pumps and a full tank, that is when I found out that the selector valve did not work as far as fuel delivery, but the gauge did.
I have not ran out of gas in more than 25 years, if I have to monitor both tanks to keep from doing that again I will. Keep in mind the front tank ran out reading 1/4 of a tank.
I have fixed the selector valve since then but do not trust the factory gauges no longer. Plus the look would be kind of neat to my taste anyways. That is why I had asked if there was a way to monitor both tanks at anytime, if hooking up one aftermarket gauge will achive this, that is the way I will go. So the question still is could I use a aftermarket gauge in the place of the stock gauge and switch back and forth for a true reading?

 

You would have to find a guage that would read in the range of ohms that the factory sending unit uses. Otherwise, troubleshoot,fix or replace the sending unit that is currently installed. They are not the best of quality or reliabilty. I still don't understand the need of knowing what is in both tanks at the same time if you run off of only one at a time. You might not be that bright as you say but as you can see, I'm thick headed. lol.

 

I installed a fuel gauge on a S10 years ago and it had to be ordered so as to match the ohm's of the vehicle. The store was just out of stock on that particular item was the reason it needed to be ordered.
So I am guessing that the parts place will have what I need to match the spec's of the system. There is no need to know both tank levels at the same time, but I have had such a time out of the factory gauges, all of them that I am at the point of just going to all aftermarket gauges. I really dont even need both tanks, but I do want to know the true amount of fuel in either tank. I also think a home made dash that contained all the temps and such would be awsome.
When one tank is in operation, I know the pumps are off, but is it impossible to get the reading that operates the gas gauge?
Another question, I am considering making a flat bed truck and will be using a fuel cell, since the pump in the tank is low pressure can I use a conventional electric fuel pump, or do they make a fuel cell that has a pump in it already?
I like the look of some of the flat bed 4x4 trucks. I have a friend that welds and has all the metal I need to make the frame work for the truck bed. This is not my full time truck any longer and can try a few things like that.

 

The fuel level sender can be active at all times if the fuel level wires are bypassed around the tank selector switch.

 

ok, I know there are a couple of different dual tank systems out there based on year and engine, so this info is relating to the dual tank system in my '88 F-150 with the 5.8 EFI engine.

I have the rocker switch on the left side of the dash, and the six port selector valve under the chassis.


the switch on the dash controls two things, Which Tank's fuel sender gets connected to the guel guage, and which in-tank pump gets turned on.

It is very do-able to get the two cables from the fuel senders coming into the switch, and connnect them to two seperate fuel guages.

the switch would then still be used still select which in-tank pump is turned on and therefore which tank the fuel comes from.

the only catch is that ford fuel senders are backwards from most other manufacturers. You will need to find guages that work with the ford fuel senders. you will not be able to use "off the shelf" guages from the autoparts.
a "standard" guage from the autoparts connected in our trucks would read backwards (Empty when the tank is full, and Full when the tank is empty.


check autometer guages for a compatible model.

 

Now we are getting somewhere, both of the above post answer my question. Thank you very much. It seemed logical that it was possible but I just wanted more opinions on the method of doing it. Again, thank you for your time to answer. By the way, our trucks are set up the same, I have a 5.8 duel tank setup as well and it is a 1988 F150.

 

LOL Frederic. Stop doing this...you've blown my mind again That's such a neat idea Definately go ahead with the LED tank indicator, and maybe instead of using just a 2 single LEDs, you could use a 7-segment LED numeric component It'll look much cooler I suppose you could have it toggle between displaying F for the front tank, and R for the rear or A fo r after (R looks like an A on those displays)...maybe a B for back tank, or go with a 1 and 2 type assignment.
Did you simply just assemble a flasher or flip-flop circuit to trigger the relay?
I'm thinking about doing this myself, it's so easy and kind of neat

 

I used a 555 timer, set for a 50 % duty cycle, set for 5 second pulses via the R/C parts, driving a 2N2222 NPN transistor (any generic NPN will do) to in turn drive the relay.

It was like... six parts.

 

LOL I was gonna throw in the 555, figuring you had probably used it I remember building tons of different flasher circuits with the 555 on breadboards for fun as a kid.