my gas gauge quit working, It has a new tank and sending unit. where should I check to fix it?

 

This may help get you started, https://www.garysgaragemahal.com/198...s--bronco.html


It would help to know what truck you have ????

 

Definitely going to need more details, please.

What is the gauge doing? Is it totally dead, pointing far to the left? Is it reading pegged high to the right?

Does your truck have oil pressure and coolant temp gauges, or idiot lights?

How long ago did you replace the tank and sending unit? Was the sending unit replaced due to an indication problem? Or was it working normally but you decided to replace it because you had the tank out for some other reason and "While I'm in there" syndrome got you? Do you still have the old sender?

Single or dual tanks? If dual, is the problem confined to one tank?

What is your favorite color?

What is your shoe size?

 

you can do an ohm test on the connectors to your sending unit and see what it is reading. I think it should be in the range of 10-73 ohms.
If it pegs one or the other it's possible it's a bad ground. Can't really do a accurate test with the ohms unless the sending unit is out.
using a known good ground to the one connector will at least give you an idea if the sending unit went bad or not.
or find the sending unit wire to the cluster and run a continuity test from the front to rear.

 

1982 F150 the needle is all the way to the left. tank is 9 months old. gauges not idiot lights. thanks everyone

 

Ah, Karl...

 

Take and unplug the front tank sending unit. If your head is not too fat(mine is pretty fat and it fits) you can squeeze up inbetween the driveshaft and the tank and you can see and unplug the sending unit wire. Get a helper and turn the key to run but do not start the truck. You get underneath and take a little jumper wire and jump the two sending unit terminals. The gauge should swing slowly full scale empty or full, I can never remember which. Then take the jumper out, the guage should swing full scale the opposite direction. If it passes this test, the wiring and the gauge are good, Something is wrong with the sending unit.

 

Not trying to bust your behind, but you still haven't answered the questions quoted above. I'm just trying to gather as much info as possible so we don't send you on a wild goose chase.

More questions, too. Sorry...

What year?

Engine? (Do NOT say "yes" or I will personally slap you! )

Do you have a multimeter? Once possibility is the float has sprung a leak and sank to the bottom of the tank. Or perhaps the float has detached from the arm. I have an idea how to check, but it will involve reading resistance to ground from a connector near the brake master cylinder. Interested? I'll need more details about your truck to put together a plan of attack.

 

1982 1/2 ton yes engine 302

 

Forum Member Karl to the White Courtesy phone please....

 

From the “Still Unanswered Questions” department:

Single or dual tanks?

 

I found this looking for something else.

 

single rear tank now. both were removed and I only installed a new rear tank.

 

LOL HAHAHA

 

Ooh, this is very helpful info. I wasn't peppering you with questions just to be annoying. I'm fully capable of that with no extra help. No, I wanted to be sure of the exact steps to suggest for troubleshooting.

Take a look at pages 58-59 here:

https://www.garysgaragemahal.com/1981-evtm.html

That for 1981, but your 1982 should be similar.

Note how the signal from the sender passes through the selector switch. Even though you only have a rear tank now, that switch is still part of the indication circuit. Cycle the switch a few times in case the internal contacts are dirty or it wasn't fully seated in the rear position.

If no help, do you know how much fuel is in the tank? If unsure, add at least half a tank (8 gallons) if there is room. In the next steps, we need to be sure the tank is NOT nearly empty, as that would skew the results.

Are the oil pressure and coolant temperature gauges working normally? Those two gauges have the same power supply as the fuel gauge, so it's important to be sure. If all three gauges are inop, we will need to shift gears for troubleshooting. Ignore the ammeter, as it is a totally different creature.

If the temperature and oil pressures gauges work, disconnect the plug from the back of the tank selector switch. I had previously mentioned a plug under the hood, but since your truck previously had dual tanks, it's way easier to work from the selector switch.

Note the 5 wires on that plug. Match them up with the view at the upper corner on page 58 of the wiring diagram. I'll reference the numbers, not the wire colors, in case of any changes from year to year.

Connect a jumper between wire sockets 29 and 675. Nothing fancy needed, even a paper clip would work. This simulates the normal circuit through the switch. If the gauge works now, the switch is bad.

If still no joy, briefly connect a jumper between socket 685 and a good ground. The outer shell of the cigarette lighter is usually good for that. The jumper simulates the sender being a little higher than full. The gauge should rise above the H mark. This is higher than normal so don't leave it too long, but 10 seconds or so to watch the gauge respond is fine. If no response and the ground was good, there's a problem with the gauge itself (not very likely) or in the circuit from the dash to the switch.

Next, set your meter to read ohms, on a range 0-100 or whatever range is closest. Touch the leads together to test the meter. You should see close to zero.

At the selector switch plug, measure the resistance between socket 675 and ground:

Approximately 10 ohms would mean the sender arm is all the way up, but I doubt you'd see that.

Approximately 73 ohms means the sender arm is at the bottom of the tank. If that's what you read, the float may have filled with fuel and sank to the bottom of the tank. Or the float may have come loose from the sender arm. Either way, if you see around 73 ohms, the sender arm is sitting at the bottom of the tank and will need some love. The electrical portion of the sender is probably still good, but unfortunately not the mechanical side.

If you read significantly more than 73 ohms, either the sender has failed electrically, or there's a problem in the wiring between the selector switch and the tank, or from the tank to ground. G701 is the ground for the indication circuit, and is located under the dash. Many circuits use this same ground, so you'd have multiple problems if the ground itself was bad. All bets are off if you modified the wiring at the tank.

Keep us posted.