Chevy C20 fuel gauge not working! HELP!

[chevysonly]

I have been working on mechanical stuff on this beast and now I'm tackling the electrical. The fuel gauge reads almost full with key on AND off! Occasionally, the needle will move to over full when turned on. I have checked the sender (float, etc.) - it works fine. However, it doesn't have a ground wire... ?? Retraced the tan wire that supposedly runs to the fuse panel - no cracks or breaks. Here is part of my dilemma: when the tan wire runs up toward the fuse panel, it doesn't plug into it. It goes into a wiring harness/cluster. What gives?

[LockDoc]

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Make sure that the cluster ground wire is there and connected. It clips onto the dash behind the cluster. (see picture) You might want to slide the clip off and back on to make sure it is making good contact. Let us know if that makes any difference or not....

LockDoc

[chevysonly]

Thank you for the reply.
OK, I checked behind the instrument panel and found the ground wire; sure enough, it was unclipped! I scuffed it a little before reclipping it in order to ensure good contact. There doesn't seem to be any difference in the position of the fuel gauge needle. Shouldn't it drop back to "Empty" when the key is turned off?

[randy500]

Get one of those small LED flashlights at harbor freight and just look down into the tank through the filler neck to see how much gas you gave...or use a wood dowel to measure the gas.....

Or get a multi-meter while your at harbor freight and read resistance at the cluster gauge feed wire and check voltage to the gauge. Gauge reading is zero to 90 ohms

[LockDoc]

Originally Posted by chevysonly

Thank you for the reply.
OK, I checked behind the instrument panel and found the ground wire; sure enough, it was unclipped! I scuffed it a little before reclipping it in order to ensure good contact. There doesn't seem to be any difference in the position of the fuel gauge needle. Shouldn't it drop back to "Empty" when the key is turned off?

No the gauge doesn't return to empty. It pretty much stays where it was when the ignition was turned off. It may move a little but not much....

LockDoc

[chevysonly]

Alrighty, then! I manually checked the fuel level and it's at about half. Tried the ohmmeter, and it pegged to the right! I will include a pic of the meter I used (not connected). Just imagine the needle on the right side.

[chevysonly]

I'm not sure my pic loaded.

[LockDoc]

Originally Posted by chevysonly

Alrighty, then! I manually checked the fuel level and it's at about half. Tried the ohmmeter, and it pegged to the right! I will include a pic of the meter I used (not connected). Just imagine the needle on the right side.

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Picture came through just fine. I'm not sure what the pegged Ohmmeter means. I'm not that familiar with them. Maybe someone else will chime in on that.

LockDoc

[chevysonly]

In this case, it means that the needle went all the way to the right.

[Old_Gold]

If the meter went tip the right, you are at zero ohms. Not sure if it thinks it is completely full, or empty, but it may be a faulty sending unit if you are at half a tank

[franken]

For Ohms, or the top on the meter pic, or Ohmega, all the way to the left is infinity, and the right zero Ohms or zero resistance. Get lazy. a DVM is easier to read.
Pop the sender out of the tank and have a look, measure into and out of it or take measurements in between.
Regardless, depending on fuel level or float level the needle and voltage at the gauge should vary to ground.

Welcome to automotive electrics. Think aobut working on a (today) modern vehicle w/ 3 miles of wire and 10 little computers running things when they're 40 years old. Yikes! Then again at that time an EE will be 4th grade.

[LockDoc]

Originally Posted by chevysonly

In this case, it means that the needle went all the way to the right.

Yeah, I understood that. I should have said that I don't know what it indicates...

LockDoc

[VetteVet]

Your sending unit must be grounded to the tank and the tank must be grounded to the frame. Then the cab must be grounded to the frame to complete the path back to the battery ground.

If the tan wire isn't on the "fuel" terminal on the fuse panel, the gauge isn't connected to ground through the sending unit. Unless someone has wired the sending unit directly to the gauge. Since you can't find the end of the sender wire, you might try running a temporary wire from the sending unit to the FUEL terminal.

Turn on the key and run a ground jumper to the fuse panel terminal, labeled FUEL, and the gauge should go to the far left (empty).

If the needle doesn't move then the gauge is probably bad or the wire from the fuse panel (fuel) terminal may not be connected to the gauge. It goes to the no. 4 pin on the cluster plug.

If the fuel gauge needle never moves, then the gauge probably isn't getting power from the fuse panel. Does the temperature gauge move?

Never put power on the sending unit wire

This may cause the sending unit resistor to become hot enough to ignite fuel vapors in the tank and you'll have a very bad day.

How are you connection the volt/ohm/meter?

[chevysonly]

@VetteVet

1) There is another wire connected to the FUEL terminal at the fuse box. It appears to be coming from what I would normally assume is the direction of the fuel gauge; however, I am learning not to assume anything when it comes to automotive electronics.

2) The temp gauge doesn't register anything either. It is pegged to the right, past H.

3) Connecting a hot wire to the fuel tank is starting to sound like a reasonable idea! GRRR..... just kidding!

BTW, I have read several instructions on testing the fuel sender and I want to make sure I did it correctly. First, I removed it... next, am I supposed to connect one end to the sending post and the other end to the housing of the unit, or to another ground?

Additionally, I want to thank ALL Chevy enthusiasts that are chiming in to help!