1968 Chevelle help

[LoHo]

Hey guys, I've owned a '68 Chevelle Malibu for several years and have enjoyed the simplicity of the mechanism. However, I have a problem that I can't figure out.

Some time ago the fuel gauge began to fluctuate widely, and has since been stuck on FULL. The only wiring I can see is a ground wire from the sending unit. I realize that the likelihood is that the rheostat has given up after 45 years, but I don't understand how the gauge in the dash gets the information from the tank. Is there another wire somewhere? As far I can tell from the over-general manual I have, the ground from the sender to the frame is the only wire, but there must be something from/to the gauge, right?

[crazy steve]

Most automotive gauges of that vintage are fed a 'regulated' power source (usually a reduced voltage of about 9v) into one side, and the sending unit is generally the ground side of the circuit. So there should be a wire from the sending unit to the gauge. If you verify that, then it might be the 'regulator' has failed; although if the car has a temp or oil pressure gauge and those are working right, the regulator is good. But a lot of cars that vintage only had idiot lights, not gauges.

I believe that if the wire to the sending unit goes to ground anywhere, that will cause your problem.

[XS1100 Newbie]

Positively a grounding problem, whether it is the sending unit, or the power supply. I think that the sending unit does have it's own power wire. It may involve removing the instrument cluster, and identifying the wire on the plug that goes to the gauge, then read it out to ground.

[DiverRay]

LoHo,
I have a Chiltons' that covers that year. Let me try and look up a wire diagram to see if I can tell you what color wire to look for. Give me about 1/2 hour...

[motoman]

Hey guys, I've owned a '68 Chevelle Malibu for several years and have enjoyed the simplicity of the mechanism. However, I have a problem that I can't figure out.

Some time ago the fuel gauge began to fluctuate widely, and has since been stuck on FULL. The only wiring I can see is a ground wire from the sending unit. I realize that the likelihood is that the rheostat has given up after 45 years, but I don't understand how the gauge in the dash gets the information from the tank. Is there another wire somewhere? As far I can tell from the over-general manual I have, the ground from the sender to the frame is the only wire, but there must be something from/to the gauge, right?

Hi Larry, 'old school' way of checking for gauge functioning or not was to ground gauge and if needle went full up, gauge itself was workin fine. Sounds like this may have done that on its own. If the 'hot' lead on the sending unit itself came unplugged, corroded and broke off and is grounding to tank or other ground source, the same result as testing gauge. Can't remember for sure, but unfortunately there's not enough room to reach your hand top-side of that tank to feel for an unattached wire. If you can loosen the tank strap bolts and let the tank drop a bit, this may give you enough room to access the area. If you need to remove the sending unit, the tank will have to be dropped down substantually lower of course. Your saying the gauge fluxuated wildly prior to its 'stuck on full' leads to suspect of a wire grounding between gauge and sending unit.

[DiverRay]

LoHo,
Sorry, but it seems my books stop at '72, I can't help with the wire color. The tests listed will work, and at least tell you if you have a short or open.

[bikerphil]

Here's the 68 Chevelle wiring diagram, click to enlarge...

[MPittma100]

Chevelle

There is definitely another wire that goes to the tank other than the ground strap. How else would the guage recieve a signal? It is there somewhere and, as was mentioned, you should ground it when found and see what the guage response is (key on). Guage reads full when grounded, empty when not indicating no guage problem.

MP

[MPittma100]

Chevelle

There may be a removable panel/plate in the trunk under the mat to be able to gain access to the sending unit. Check that before removing tank.

MP

[ccogswel]

If your gas gauge is the only one reading full all the time you have a ground issue. Could be the fuel sending unit in the tank. One way to tell is unplug the one wire off the sending unit in the tank. Then look at your gas gauge to see if it's not reading full. If it is isn't reading full you have a bad sending unit. If it's still reading full you have a grounding connection somewhere from the wire from the tank to the cluster. Hope this helps.