Is there a way to bypass the fuel tank selector switch to only use one tank? I removed the front tank from my dads truck. I have the switch on the aux position and the gauge goes past full. I put a new sending unit in the tank.

 

A little more info would be helpful.

There are major differences between years with the factory dual tanks.

 

It's a '77 F100

 

Physical fuel bypass is easy... simply run a length of rubber line around the selector valve so the engine can only pull from the desired tank. I did this on my '78 for a while. Electrical means finding a wiring diagram or tracing the wires and bypassing. Not sure how to do it on a '77.

 

I have removed the switch from under the cab. I have the wire connected from the sending unit to the wire from the tank switch. I'm just wondering if I need to unplug the switch from the dash and wire it direct.

 

The short answer to the one and only question asked in your first post is "Yes". Blue and White went on to explain how to proceed with bypassing the fuel selector switch.

Sounds like there may be more issues with the fuel system on you truck than you first addressed as well as questions you didn't ask. Long distance trouble shooting is always difficult, doubly so without all pertinent information. All the members here want to help and share their knowledge. The more information you can offer the more help you will receive.

In trying to answer questions you didn't ask:

There has been a fair amount of discussion on this site as to which tank is which on these trucks. As I remember, the factory rear tank is the main and the factory front tank is the aux.
Did the truck come factory with dual tanks? Is the switch you refer to the factory dash mounted switch, by the heater controls, or is it a floor mounted selector switch?

Have you tried putting the dash switch in the "main" position? If so, what does the gauge read?
Why did you replace the sending unit in the rear tank?

A gas gauge reading well past full can indicate a shorted or grounded wire from the sending unit to the gauge.
What did you do with the sending unit wire from the front tank?
Why did you remove the front tank?

With solid answers to all these questions we will have a better chance of figuring out what is going on with your truck.

Good luck.

 

It did come with factory dual tanks, switch is by the heater controls, I replaced the sending unit in the rear tank due to it was rusted out and the float had deteriated due to old age (the original since 1977), and I removed the front tank cause the truck will only be driven on the weekends and I didn't like it. And if the switch is put on main, it doesn't read at all.

 

OK, that gives us a starting point.

When everything else is checked out and working correctly there is no need to do anything with the dash switch. You can leave it in the position for the rear tank (main, as I remember) and everything will be fine.

Still need to know what you did with the wire from the front tank sending unit. Lets make sure it's isolated and not grounded.

Do not do anything with the wires you disconnected from the fuel selector switch (under the cab). Make sure they are clear and not contacting anything.

Now, take the sending unit wire off the rear tank. With the sending unit wires from both tanks disconnected and not grounded, turn the key on and check the gas gauge in both positions of the dash switch, main and aux. The gauge should rear empty for both tanks.

The next steps depend on how this check turns out.
Get back to us and we can go from there.

 

I have deleted the switch from under the cab. It's in the trash

 

That's OK. You disconnected the wires and left them hanging, right?

 

I connected the wire from the rear sending unit to the single wire from the under cab switch.

 

Don't connect anything to the wire that went to the under cab selector switch
For now, let the wire from the under cab switch hang free and keep it from contacting ground.

I'm not clear on the rear sending unit wire you are talking about. Typically there is a single wire that runs to the rear sending unit and comes out of a larger loom that runs along the driver side frame rail. There should not be any splices, junctions, etc. in this wire.

 

Got it fixed. My dumb self had the switch on the dash on aux.

 

Glad you figured it out.