I have a 65 F250 (F25DK672543) (129 M F250 E81 N 24). It has three gas tanks on it. I have only been using the tanks in the rear because the tank behind the seat had a hole in it. I was able to remove the tank in the cab on Saturday and patch the hole. I cleaned it out very well and installed. I put two new inline fuel filters on as well. I hooked up the sending unit. I put in 10 gallons of gas and the tank is doing great. I don't have any leaks or fumes in the cab. My new problem is with my gas gauge. I have not been able to ever use it. With the key in the on position the needle reads all the way past the FULL position with 12 gallons of gas. I pulled the instrument cluster and I have a orange wire and black wire hooked up to the gauge. I went back to the sending unit and made sure I had a good ground. I then pulled off the orange wire and grounded it and the gauge acted the same. I check my orange wire with my meter and from the sending unit to the gauge and it is good. I had another gas gauge and I tried it and it did the same thing. All the other gauges on the cluster are working properly. I am wondering if my gauge is bad or if I have something else wrong in my wiring. Any help that you could provide would be nice. I would love to know how much gas I have in the truck. Thanks

 

Jon:
The reason the gauge reads full when you ground it, is that you're completing the circuit without going through the sender (which is a variable resistor). This sends a full 12 volts to the gauge and, so, it reads full. The problem is not lack of voltage to the gauge (wire continuity), it's too much voltage. So there is a short in the system somewhere, such as a bare wire touching ground or in the gauge or sender. You probably ruled out the gauge when you tried another. So look for a short in the orange wire (grounded out) from the sender to the gauge or your sender is bad.

 

The sending unit could be the culprit as well.

Based on you previous post, you have already proved out the wiring and gauge by grounding the orange wire at the sending unit and having the gauge show "full", as well as having the same results with a second gauge.

The only part of the circuit you haven't proved out is the sending unit.
You can test the sending unit by removing it from the tank, hook the orange wire to the sending unit, running a ground wire from the sending unit to the truck and working the float arm with the key turned on.
With the float level with the sending unit mounting flange the gauge should read "full" or a bit above. With the float arm at the bottom of it's travel the gauge should read "empty".

Be sure the float arm on the sending unit didn't get bent while it was out of the tank. A bend in this are can lead to incorrect readings.

Good luck.

 

The only fuel tank available for 1961/66's was the in-cab tank. The other tanks were probably added by an RV dealer.

The in-cab tank has been reproduced, it's the same 1961/72 F100/750.

D7TZ-9275-G (replaced C1TZ-9275-K) .. In-Cab Fuel Tank Sending Unit / Obsolete ~ A few are available NOS

Applications: 1961/77 F100/750.

Carpenter has a reproduced in-cab sending unit, but it's made in China.

 

I resolved my problems that I had. I did have a wire inside both gas gauges touching ground. The other problem I had was that I had the float on the sending unit in backwards. Thanks for the tips. I am so excited to know how much gas I am carrying with me now.

 

It is always good to know how much gas you have. Helps to avoid social blunders.

 

1965 f 250 installed new sending unit tested good 10=70 ohms (out of tank) filled tank and gage shows 1/4 tank if i ground su wire at tank gage goes to full as it should (key on) i put a gage tester on the the stock in dash gage and at 15 ohm = empty 1 ohm =full 7.5 ohm = 1/2 so that's backwards from factory which is 10 ohm = full 70 ohm = empty so my full tank at 10 ohms is correct (ohm wise) at 1/4 on gage so as my tank empties it will go to full gage Question is the gage bad, polarity reversed, ivr bad, all grounds and wires are tested good, any thoughts? i dont know of any gage that operates in that ohm range, so im thinking voltage or gage?

 

Here is a thread to read through. You really need an analog meter to check this old stuff. Fuel gauge issue - Ford Truck Enthusiasts Forums (ford-trucks.com)

 

I am having a similar issue... I recently had my fuel pump replaced and ever since my gauge has been stuck pass full. Something is also killing my battery every night. Cant seem to figure it out.

 

Your profile says you have a 94, F150. If that is the case you are in the wrong forum. If you have a 61-66 then your problems are unrelated to the fuel pump. Let us know what you got. But if it is a 61-66. If all other gauges are working normally you have a short in the orange wire going to the sender in the tank. If all the gauges are going full travel your ICVR is bad.
Put you hand on the voltage regulator after the truck has been off for am hour or so, if it is warm then something is stuck in it and it is draining your battery.