There were sopme listings earlier about fuel gauge problems and I came
across the following on an
AMC website (http://www.amcwc.com/techtips.html) . I hope this helps.
Fuel Gauge Problems
Troubleshooting 68/70 Fuel Gauge Problems.
If your gas gauge was working OK, but all of a sudden it quits working
altogether, or the needle is reading LOWER than the amount of gas that is
really in the tank, then this is the fix for you. 68/70 AMX and Javelin fuel
gauge test. This will be a process of elimination. Let's start with the
gauge itself.
Put the car on jack stands and let the rear suspension hang down. Remove the
passenger rear wheel. Doing this will give you plenty of access to the fuel
tank sending unit. First things first. Is the yellow feed wire connected to
the sending unit? If not, make sure the terminal on the sending unit is
clean, also make sure the yellow wire socket is clean and that it fits
tightly on the sending unit terminal. Check the sending unit black ground
wire. Make sure it is clean and connected. Turn the key on and check the
gauge. If it still doesn't work, then try this next test. Remove the yellow
feed wire from the sending unit. Do not remove the ground wire! Find
yourself a 5 to 6 foot long jumper wire the same gauge as the yellow sending
unit wire, and strip both ends of the jumper back about 1/2 an inch. Take
one end of the jumper wire and push it into the yellow feed wire socket.
Bring the other end over to the driver side of the car. Sit in the car, turn
the ignition to the "ON" position and touch the end of the wire to any one
of the scuff plate screws. What you're doing is "grounding the gauge". If
the needle goes all the way past "full", then the problem IS NOT the gauge.
if the needle doesn't move at all, then the problem is in the feed wire from
the gauge to the sending unit. Here's where it gets interesting. In 70 there
was an option known as a "low fuel warning system". It was designed to warn
the driver when the fuel level gets to 1/4 of a tank or less. When the fuel
level gets to 1/4 tank, a light flashes in the center of the fuel gauge. If
you have this system in the car, then chances are this is the reason why
your gas gauge won't read at all. If you have a 68 car, or if you don't have
the low fuel system in your 69 or 70, then the problem IS the sending unit
in the gas tank. (usually the float, or a burned out unit all together) To
determine whether or not you have a low fuel warning system, look closely at
the face of the fuel gauge. Between the "F" and the "E" will be what looks
like a tiny rectangle slot. If you see this slot, you have a low fuel
system. It operates off of a relay located under the dash directly right of
the steering column, secured to the dash frame with one screw. It has a
4-wire plug off the relay that connects to the back of the instrument
cluster circuit board. It is not enough to simply unplug the relay and solve
the problem. You MUST COMPLETELY REMOVE the 4-wire harness from the back of
the circuit board. The key to doing this correctly is dependent on the
orange light wire which is part of this 4-wire harness. Notice how the
orange light wire is plugged into a black plastic socket? The socket is held
onto the circuit board by one of the nuts that holds the fuel gauge into the
cluster. Remove the nut and take off the socket. Make sure you put the nut
back on and snug it down! By doing this you have reconnected the original
circuit, only without the low fuel system. Put your cluster back in and make
sure your main harness plug in connected. Turn the key on and check the
gauge. If it works, then your problem was a burned out low\ fuel relay. If
you don't want to go searching for an NOS replacement relay (used relays are
not reliable, nor are they accurate) then just put you dash back together
and leave it alone. Even when the low fuel system is working correctly, it
can be a real annoyance as the light will continue to blink until you decide
to fill the tank. I believe this was really designed for long trips where
you don't pay a whole lot of attention to the gauge as you're cruising
along, and starts to blink when you're low on gas, or reminds you to wake up
and go get some gas! I hope this helps answer questions on this subject. As
you can see, these are fairly simple tests to tell you EXACTLY where the
problem is and how to fix it. Good luck!
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