C2 fuel gauge question

[Pete Lovrovich]

After hooking up my guage cluster and filling the tank with fuel, I find my fuel gauge going from the empty line to below the empty when the ignition is turned on. For some unknown reason to me it wants to travel backwards. Is this a matter of wires crossed or??
Thanks for any advise you may render to help.
Pete

[Wayne C.]

Re: C2 fuel gauge question

First thing to check might be to make sure you connected the instrument panel's ground... should be a spade on the cluster panel itself near top center connected to a black wire with a white stripe. You might be able to just check continuity from the cluster panel to a frame ground (with a multimeter on the ohm scale, using test wires) to ensure that you're getting a good ground.

I think the gauge terminals are marked "I" (for Ignition... green wire) and either "S" or "T" (for Tank... brown wire) respectively. Unfortunately, if you got them reversed at the gauge or at the tank it could have burned out your tank sender.

[Chip Levick]

Re: C2 fuel gauge question

My gauge does the same thing! When the tank is full of gas - the gauge reads empty and when the tank is empty - the gauge reads full. I checked the wiring at the tank and the terminals are made where you can't put them on incorrectly. I checked my instrument cluster and cannot find any ground wire. Maybe that is my problem - yours also.

[Wayne W.]

Re: C2 fuel gauge question

It is obvious that it is wired wrong, either at the guage or the connector to the rear body. The sender is simply a center tap. Voltage is applied to a resistor. On one end of the resistor is 12 Volts on the other zero or ground. The slider rides on the resistor and picks off the voltage at some point in between. If it is working, but reading backwards, it has to be wired wrong.

[Wayne C.]

Re: C2 fuel gauge question

To expand on my prior post:

My understanding is that the fuel gauge reads the differential between the resistance in the tank sender circuit (the green and tan wires plus the sender's vaiable resistor make up that circuit) and frame ground. Frame ground is attained through the contact of the case of the gauge to the metal instrument cluster panel. The greater the differential, the higher the reading on the fuel gauge. Relatively, the frame ground is zero while the tank sender resistance varies from 0 to 90 ohms depending on the fuel level.

The cluster panel is supposed to be grounded via the black/white wire I mentioned in my prior post, somewhere near the rear top center of the panel. So if you use a multimeter to test the resistance from the back bare surface of the instrument cluster panel to a known frame ground, you should see a zero-ohm reading (similarly, a reading from the case of the fuel gauge to the back of the cluster panel should be zero ohms)... if not zero, then the instrument panel (or the gauge case) isn't properly grounded and therefore the fuel gauge will read incorrectly.

My guess is that a high ohms reading from the cluster panel to frame ground (infinite, which means no ground connection; or a reading above 90 ohms; or even a reading that is higher than the current reading from the sender's variable resistor, which is a range of 0 to 90 ohms depending on the fuel level) could result in a below-empty gauge reading.

[Wayne W.]

Re: C2 fuel gauge question

I know what you are trying to say, but these gauges are in effect volt meters and do not read resistance but voltage. As I said 12V is applied to one end and the other is ground. The sender picks its voltage signal off of the resistor. That voltage will be somewhere between 12V and 0V. As you say, that guage must be grounded.

[Pete Lovrovich]

Re: C2 fuel gauge question

Thanks for the responses, I am out of town, but as soon as I return, I will use your advise.
Thanks,
Pete