Fuel gauge stays full

[kgoodner]

Ok I've seen a lot of posts on the fuel gauges not working right bad grounds ,senders etc.
Mine stays full when connected . Wires are correct , new sender with 5-317 ohms full to
empty. Even tested at the tank with jumper wires.
Bad gauge?
Are there any fixes for it?
Thanks for any input.
Should add its 1979. 2000 spider

[vandor]

Either a bad gauge, or the wire is touching ground somewhere. You can run a separate wire to the gauge to see if it starts working.

[spider2081]

with both wire disconnected from the sender what does the gauge read?

[kgoodner]

With both wires off gauge reads empty the low fuel light works in the right place
with the sending unit. And I tested it out of the dash and with just the sending unit
and battery. Jumped to correct terminals and sender .

[spider2081]

OK. For me your post sort of contradicts itself.
Did you remove the wires from the gauge or from the sender?
The gauge should display empty when the sender wire is disconnected from the sender. You say it does.
The gauge should read more that full when the gauge wire from the sender is grounded. You say the gauge reads full when the wires are connected.
To me this says the gauge and the wires through the car are good.

The low fuel warning light needs a ground from the sender to light the light. The sender supplies this when there is about 1/8 tank of gas in the tank. You say the light tests good. My first guess it that the wires are reversed when connected to the sender. How much gas is visually in the tank?

With the sender out of the fuel tank and its mounting ring making a good electrical ground (use a jumper wire to make the ground) let the float fall all the way down. Touch the sender wires one at a time to each of the sender terminals. Only one combination should light the light.
The remaining wire is the wire that drives the needle and the remaining terminal is the correct terminal for it to attach to. Moving the float up and down should now make the needle move correspondingly. You say you did this and it checked good.

In your first post you state the sender measured 5-317 ohms so the sender seems good, are you positive you have the needle wire connected to the post that reads 5-317 ohms, and did you measure that resistance between the terminal and the senders mounting ring?

Hope this helps

[kgoodner]

Thanks for the input I disassembled the gauge found a broken wire on on of the coils
I will now replace it

[tartan18]

My gas gauge is behaving in a similar fashion to what is posted to this point -- When I ground the two wires in the trunk the gauge properly lights up the low fuel warning light and the gauge does swing and indicates the fuel level in the tank. However with the two wires connected to the sending unit the gauge does not function at all. I suspect the gauge itself is not properly grounded ?? If this is the case what wire on the gauge harness is the ground? According to my wiring diagram (for a 1975) it appears that the white/black wire could be the ground. If this is correct then can I just splice on a new ground wire to this one? Any help would be appreciated.

[spider2081]

However with the two wires connected to the sending unit the gauge does not function at all.

Do you have the sender out of the tank? IF you do do you have a ground wire connected to the senders mounting ring?? The senders mounting ring needs to be grounded for the sender to function properly. If it is in the tank and does nothing try a jumper wire from one of the sender mounting screws to the battery ground. It i sort of common for the fuel tanks to become ungrounded over time.

[tartan18]

I suspect that the gauge itself isn't grounding to enable the aapporprite signals -- especially since I have had a few connections when I "wiggled") the wiring harness. I cannot identify what connection is the problem, Therefore I suspect that the problem is between the gauge and the harness. Any help to trace this will be appreciated. My wiring diagram indicates that the white and black wire could be the issue.

'To recap .. fuel tank and sender are new ... both have confirmed connectivity to ground with a ohm meter. If I ground either lead to the sender while it it is in the tank I get appropriate signals. I have tested the sender both in and out of the car. My car is a 1975.

Ideas ??

[spider2081]

with the ignition key in the run position.
If with both wires of the sender the gauge reads empty and the light is off that is correct.
If when you ground the gray/red wire at the sender end and the fuel warning light lights that is correct.
If you ground the blue/yellow wire st the sender end and the gauge needle moves beyond full that is correct.
also those tests say to me that the wires through the car and the gauge are working correctly.

To me the problem is the sender or the ground at the sender

[tartan18]

With my ignition key in the run position and the sender mounted in the fuel tank with both wires connected to the sender there is no signal to the gas gauge (either low fuel light or fuel level).
If I ground one of the wires to the sender's metal mounting ring the low fuel light light illuminates.
If I ground the other wire to the sender's metal ring the gauge indicates the proper fuel level in the tank.
The fuel tank and sender are grounded (zero ohms to the car's body) ... but to say it again ... the gauge does not operate with either or both wires connected to the sender's spade terminals,only when I ground them to the car's body.
Both the fuel tank and sender are brand new. My car is a 1975.

This seems to indicate that the wiring in the trunk is correct which suggests to me that the problem is the gauge's wiring. I have two fuel gauges and both behave the same. This again suggests to me that the problem is the wiring to the gauge itself. Any more ideas of what I should check?

[spider2081]

If I ground the other wire to the sender's metal ring the gauge indicates the proper fuel level in the tank.

If you ground that wire the gauge should read more than full. If it is only reading partial tank then either:
you are not making a 100% ground
there is resistance in the connections between the sender and the gauge
there is a problem with the gauge.

Have you grounded the gauge end of that wire while it is connected to the gauge to see if the needle reads different. I think the only connections for the gauge quantity are the one at the sender, the fuel gauge connector and the terminal on the back of the gauge. If one of those is loose or corroded it could be the problem.

[tartan18]

Tomorrow I will try your suggestions and let you know the results. I believe the issue is with the wiring connections to the gauge. Thank you for sticking with me on this problem.

[tartan18]

Grounding the wire at the sender pegs the fuel level fully. I am trying to figure out the wiring of the gauge connector. When I sort out the various wires I will let you know the results. All connections have been cleaned (no corrosion), no voltage drop that i can find.

[spider2081]

If grounding one wire the needle pegs fully and grounding the other wire the fuel warning lite lights I think the gauge and wiring is good. Your problem is at the tank. Either the sender is bad or It is not getting the ground it needs.