67 galaxie fuel gauge problem

[red29ny]

Just bought 1967 Galaxie conv. Gas gauge reads full all the time even when tank is empty. Looking for advice on trouble shooting this problem.
Thanks, Peter

[dmsfrr]

Does the gauge needle sit in the 'Empty' position when the car is turned off, and go to Full when the key is turned On?

Disconnect the wire on the gauge that goes back to the sender in the tank.
The needle should go to the Empty position. If it does the gauge is working and the sending unit in the tank may be stuck, shorted or the wire to it from the gauge may be shorted out to the body somewhere.
If you can get to the wire connection on the tank sender you can also disconnect it there to see if it affects the gauge reading. If it does the sender has a problem. If it doesn't the wire between the gauge & sender may be shorted.
.

[red29ny]

dmsfrr,
Thanks for your suggestion. yes needle sits on empty when key is off and goes to full when key is on. Looking behind dash I can't even see back side of gauge to locate and disconnect wire. Just today ordered 1967 ford & merc shop manual which hopefully will explain how to access back of gauge. will explore tank sender connection this weekend hopefully. Thanks,peter

[rotorwrench]

Sometimes the whole gauge panel has to come out to check instruments. I would try disconnecting the sender unit first and see what happens. Most instruments use a bimetallic that bends when heat is applied to make a needle movement. Most of the later cars use a variable resistor in the sending unit to change the current value to the indicator. Ford used specific resistance values in that time frame so if a person knows the values they can find a way to test the instrument. The sender can be checked with a multi-meter set on Ohms reading but it would have to be removed from the tank to test it.


The instrument or gauge can be checked with various voltages of dry cell batteries to see what it does. Just don't go over 6-volts. a lot of the old Fords have constant voltage regulators that cut the voltage back for the instruments.

[poolplayer1]

Most Likely a short in the tank sending unit. If you can get to the wire at the sending unit that comes off the gauge, turn the key on and when the gauge reads full,remove the wire form the sender and if the gauge reading falls to empty,eighter that wire coming off the gauge is shorted to ground or the sender has a short in it.

[red29ny]

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Update: Removed 2 wire connector from sender at tank, turned on key switch, gauge needle still goes to full with sender unplugged. Will need to find way to back of dash gauge and diagnose further. Thanks, Peter

[rotorwrench]

The fuel quantity circuit may be shorting to another power source or shorting to ground on the sender side. If the gauge checks OK the the two wires will need to be checked for shorts. A two wire system to the sender may indicate a fuel low warning system. Generally there only needs to be one wire to the sender unit unless the other goes to a convenient ground terminal in order to ground the sender body to the frame. I'd have to look at a 1967 Ford Galaxie wiring diagram to find out but I don't have one handy.

[5851a]

I believe the 67's have 2 wire plug, one wire grounds the sending unit itself other wire goes to rheostat part.

[red29ny]

Update #2: Sender does have 2 pin connector, did some wire tracing and one wire does go to ground with good continuity. second wire goes to dash area, presume to gauge. Testing unplugged connector at sender with key off, that wire is also grounded. That seems wrong to me. Once I get to the back side of dash gauge my plan is to run a test wire from sender to gauge & see what I get. Hope to do that soon. Thanks, Peter

[red29ny]

Update # 3: Ran new wire from sender to gauge. Bingo! gauge seems to work! Now need to drive and burn off some fuel I put in when I was afraid of running out. Thanks everyone for all the input.
Peter