Fuel gauge question #355

[jdl71]

I’ve read through all the faq’s. I guess I know the answer just need someone else to tell it to me. I have a gauge cluster dash. Fuel gauge parked on E. I have continuity from the tank brown to the gas gauge term end at the fuse box. The wire is not grounding out anywhere. I read around 15 ohms from the sender. I have about a half tank of gas. I have continuity from the fuse box term to the brown wire at the gauge. I have B+ on the pink wire at the gauge with key on. Still nothing. My understanding of this is if the wire to the tank is open the gauge goes to full. It never moves off E. I have 2 clusters. Both same result. I guess I need someone to confirm I have 2 bad gauges.

[jdl71]

Anyone?

[ray_mcavoy]

Four things that can cause the fuel gauge to stay on empty include:

(1) Bad sending unit.
(2) Short to ground in the gauge to sending unit wire.
(3) Bad ground connection at the gauge.
(4) Bad gauge (open "full" coil).

It sounds like you've already ruled out #1 & #2. But just to be sure, you might want to try hooking up the gauges outside of the truck just to be sure. To do that, simply hook the gauge's power terminal (pink wire) to the positive terminal of a 12V battery or 12VDC power supply. And connect the negative side of the battery or power supply to the metal cluster case. Don't connect anything to the gauge's sending unit terminal.

If that makes the gauge swing to full (or beyond), you know the gauge is good. But if it continues to stay on empty, take the gauge out of the cluster and hook the battery or power supply negative terminal directly to the gauge's ground point. If I remember correctly, that's basically just a contact on the back of the gauge that touches the metal cluster housing for it's ground connection. And if that makes the gauge work, check for tarnish/corrosion where the gauge mounts to the cluster tin. If not, it's most likely a bad gauge.

[WorkinLonghorn]

Did you check the float to see if it was full of gas? Did you pull the sender from the tank and see if it works manually moving the float arm?

Just assuming yours is similar to my '69. I can't remember my '63.

My '69 sits on empty every day since I bought it in '97 but eventually it will show the correct value, then go back to sleep. I never did figure this out. New sender, checked the wiring Etc.

[jdl71]

Originally Posted by ray_mcavoy

Four things that can cause the fuel gauge to stay on empty include:

(1) Bad sending unit.
(2) Short to ground in the gauge to sending unit wire.
(3) Bad ground connection at the gauge.
(4) Bad gauge (open "full" coil).

It sounds like you've already ruled out #1 & #2. But just to be sure, you might want to try hooking up the gauges outside of the truck just to be sure. To do that, simply hook the gauge's power terminal (pink wire) to the positive terminal of a 12V battery or 12VDC power supply. And connect the negative side of the battery or power supply to the metal cluster case. Don't connect anything to the gauge's sending unit terminal.

If that makes the gauge swing to full (or beyond), you know the gauge is good. But if it continues to stay on empty, take the gauge out of the cluster and hook the battery or power supply negative terminal directly to the gauge's ground point. If I remember correctly, that's basically just a contact on the back of the gauge that touches the metal cluster housing for it's ground connection. And if that makes the gauge work, check for tarnish/corrosion where the gauge mounts to the cluster tin. If not, it's most likely a bad gauge.

I think I can also rule out #3 as the other gauges work as do the dash lights, unless you are meaning the ground connection on the gauge itself, which you might. I’m fairly certain the dash is grounded.

I also have swapped clusters with one I had of unknown condition and tried to get the gauge I took out to work on the bench, but am going to try again using your instructions in regards to the ground on the gauge itself. Another post I read said that the gauge itself is almost never the issue but I am almost certain I have ruled everything else out. Thank you for the suggestions.

[jdl71]

Originally Posted by WorkinLonghorn

Did you check the float to see if it was full of gas? Did you pull the sender from the tank and see if it works manually moving the float arm?

Just assuming yours is similar to my '69. I can't remember my '63.

My '69 sits on empty every day since I bought it in '97 but eventually it will show the correct value, then go back to sleep. I never did figure this out. New sender, checked the wiring Etc.

I have replaced the float with a plastic one, it and the sending unit appear to be fine as I’m reading 15 ohms at the tank with about 1/2 a tank of gas.

[ray_mcavoy]

Originally Posted by jdl71

I think I can also rule out #3 as the other gauges work as do the dash lights, unless you are meaning the ground connection on the gauge itself, which you might. I’m fairly certain the dash is grounded.

Yes, I was referring to the ground connection for the gauge itself. I just took a look at one to refresh my memory, and as I had thought, the gauge has a small metal contact on the back (right between the 2 studs) that simply touches against the metal cluster housing to connect the gauge to ground.

Originally Posted by jdl71

I also have swapped clusters with one I had of unknown condition and tried to get the gauge I took out to work on the bench, but am going to try again using your instructions in regards to the ground on the gauge itself. Another post I read said that the gauge itself is almost never the issue but I am almost certain I have ruled everything else out. Thank you for the suggestions.

You're welcome! Yes, it is quite rare (but not completely unheard of) for the gauge itself to be bad.

You can also check the continuity of the gauge's internal coils with an ohmmeter. With the gauge unplugged, measure between it's power terminal and it's ground contact. Also measure between the gauge's sending unit terminal and ground contact. If either one of them measures open circuit, the gauge is bad.

[jdl71]

Originally Posted by ray_mcavoy

Yes, it is quite rare (but not completely unheard of) for the gauge itself to be bad.

I've tried 2. I guess I'm really rare.

[hotdog hound]

my fuel gauge does not work 1970 c10 i repaced the sending unit last year have 300 miles on it.Had the transmisson rebuilt now the fuel gauge does not work. si I got a fuel gauge (stock replacement) when i pulled the gauge cluster out I saw two brown wires one was hooked up the other had no end on it. there was a red wire hooked to the passanger side of the fuel gauge and a brown wire hooked to the driver side. should there just be 2 wires to this gauge?