I'm new here hopefully you guys can help me with some of the array of questions I come up with. I've got two tanks on my 78 the one in the rear. There is some serious problems. We got wires a hangen gentlemen. I was wondering if there was any manual ways to fix this without having to learn how to wire up fuel tanks. Along with my fuel gauge doesn't work. That would be nice have working on the front tank. I'm not sure of how the system works. Does the sendor in the tank send off different voltages based on the level on the float in the tank to determine fuel levels? Along with is the power in the system originated from the tank side or gauge side? Along with could somebody give me a diagram of the fuse block?

 

the switch on the dash is to switch the gauges, to switch pumping fuel use the mechanical selector on the side of the driver side seat

 

Just had a similar problem, here is the thread i posted a short while back, should get you headed in the right direction. Lots of pics to help visualize.
https://www.ford-trucks.com/forums/9...r-problem.html

To answer your question, power comes from the orange wire from the gas guage, TO the sender, then to ground through the switch which in my case was faulty hence no ground in my case.

Yes different voltages for different fuel levels, the thread has way more detail thanks to the many helpful members here my rig is running fine with the guage working fine since i finished it. Truly an excellent site with generous members.

 

You guys are fast! Thanks Mechanical switch? What does this thing look like? What are it's dimensionS?

 

Can't speak for other trucks but on my frankenstein i have a factory electrical toggle switch under the dash on the left side of the steering wheel, that is for main and auxillary. To change between tanks ( in my case a mid tank and a rear tank ).

There is a valve, some are electrical and some i think are not on the chassis near the mid tank on my truck.

Don't know if mine works you can see pics of it in my thread, since i only have the mid tank.

My particular electrical switch can be ordered through Dennis Carpenter's catalog.

Others have said there is a factory switch located on the ventilation switch cluster.

Luckily my sender was working so i only had to replace the float with the updated non leak one and the gaskets, run a new ground wire from the sender to ground leaving the old ground wire attached and that solved my problem for less than $20.00 with shipping for the float.

I'm new to trucks and the members here were very patient and helpful with a noob like me, if it wasn't for them i'd still be scratching my head trying to fix it.

 

Link to my thread posted again in case the first one can't be seen.

https://www.ford-trucks.com/forums/9...r-problem.html

 

On 1973/74's only, the manual fuel tank selector valve (D2TZ9189A) is mounted to the floor just to the left of the drivers side of the seat.

This manual valve has a handle on it that is used to switch the tanks.

The 1973/74 dash mounted fuel tank selector switch (D3TZ9A050A)...switches the dash gauge...only.
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1975/79's do NOT have this setup (if factory original), because the D5TZ9189B .. Fuel Tank Selector Valve and Solenoid Assy which is mounted on the frame rail...does both.

1975/79: When the dash mounted D5TZ9A050A .. Fuel Tank (Toggle) Switch is flipped, it switches the tank and the dash fuel gauge.

Note: D5TZ9189B and D5TZ9A050A were used on 1975/79's only.

The two parts used 1973/74 are not the same.

 

Thank you. I looked everywhere for that dam switch. guess it's invisible. Where is the solenoid located?

 

douger, the actual fuel valve / solenoid thing is (should be) mounted to the front side of the frame cross member just ahead of the rear tank (at least that's were it is on my '78). It should have 3 rubber lines connected to it as well as an electrical wire.
the fuel switch on your dash (RH side of HVAC controls) switches this valve and also sends the signal from either tank to the gauge.

 

1975/79 F100/350:

D5TZ9A050A .. Fuel Tank Switch / Mounts into the heater control panel, on the opposite side of the blower switch.

D5TZ9189B .. Fuel Tank Selector Valve and Solenoid Assy / Mounts on the left (drivers) side frame rail.

 

On a 79 F-150 the solinoid is located on the cross member directly in front of the rear tank.

 

Does anyone know where to buy one of there fuel tank selector valve (D5TZ9189B)? I need one but I can't seem to find one. Tousley Ford has the part number but they say it's discontinued.

 

Bought my first Ford truck a couple weeks back and trying to learn the ropes of mechanics. One of the quirks I've found on my '77 is that the Auxillary Tank has been disconnected. When the selector is switched from main to aux, the gauge seems to give a proper reading and shows there's half tank of gas in the aux tank.

What are some reasons it would be disconnected? What should I consider or look at before attempting to hook it up again?

 

Not sure why they'd disconnect it, except maybe it wasn't drawing fuel from the tank when they switched the tank selector switch. Only thing I can see that you'd want to check before hooking it back up, is to make sure the gas that's in the tank isn't bad, and won't gum up your carb and filter. If it's registering that it has fuel, doesn't sound like the sending unit is bad, but it's difficult to say. That tank solenoid looks like it's seen it's better days. I just had to remove wiring from the firewall all the way back to the tail lights and take out PO splices, and re-solder the wires and put heat shrink over them, now it's working great.