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I tested the guage on my 66 and it works. I ordered a new sending unit, installed it, and still nothing. Should I cut off the plug that plugs into the sending unit and attach wires directly to the terminals? Maybe the plug its self is bad?
 

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I tested the guage on my 66 and it works. I ordered a new sending unit, installed it, and still nothing. Should I cut off the plug that plugs into the sending unit and attach wires directly to the terminals? Maybe the plug its self is bad?
Unless I am missing something if you tested the gage at the plug then its not the wiring.
 

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How did you test the gauge?

Did you also test for voltage going to the sending unit? Should have 12 volts to one of the sockets in the plug.
 

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How did you test the gauge?

Did you also test for voltage going to the sending unit? Should have 12 volts to one of the sockets in the plug.
I'm trying to remember what I did. One wire ground and one in the plug. Turned car on and the Guage moved. I didn't test the sending unit yet. I will say, when I turn the key on the Guage goes to past full and honestly, it may have done that when I tested the Guage before. I'll do that again as well.
 

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Yeah I spent a lot of time under my tank trying to rig up a test. Part of the problem is the plug doesn't easily attach to wires. Part is you can't see the gauge. Part is you can't test the sender separately. Part is even if you figure it out, by the time you stand up, you forgot.
 
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On mine one of the plug wires runs up into the trunk and grounds on a bolt. You can climb in there and check it out.
Which also means that there is only one wire, the power wire, coming from the gauge. It goes through the sender, meeting varying resistance, comes back out, finally grounding in the trunk.
 

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I recently installed an aftermarket fuel gauge in my '65 galaxie, and after the installation the gauge would always read past full. I tried everything I could think of, I checked my new wiring, the ground, the sender which the previous owner installed; nothing worked. Then I finally figured out that the poles on the sender were reversed, so I switched the wires on the original plug around and it worked perfectly after that.
 

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Check the tank for ground also. The tank is sealed around the trunk when installed years ago, and the bolts acyually make the ground. If rust, age or whatever has ruined the ground, the gauge will not work. When you test the gauge out of the tank, you hook a ground wire to it.
 

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I ordered a sending unit from Ecklers and it was advertised as genuine Ford part. What I received was a made in China version that has been very inaccurate since installation. Always reads a quarter tank low. Very possible you received a faulty sending unit. I don't order anything from Ecklers or Mac's unless it's my only option. Hope you get it figured out.
 

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How did you test the gauge?

Did you also test for voltage going to the sending unit? Should have 12 volts to one of the sockets in the plug.
Working from memory here, but I think the constant voltage regulator in the dash to the gauge only puts +5VDC on the gauge itself and too the sending unit. The sending unit tested outside the tank with a volt ohm meter should read somewhere around 7 to 10 Ohms full and 14 to 20 Ohms empty I beleive. Could have that backward, but I know it's fairly low. Yellow / White wire goes to the + side of the sender and the black wire goes to ground to the Frame or Body.
 

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I checked it again today. Switched the plug around to make sure the ports were correct. It didn't even start when I switched it so I at lease have the plug on the correct poles. Now, the needle goes to over full then it kind of just falls to past full, if that makes any sense at all. I can try to get a video of it. Maybe a bad Guage?
 

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If you ground the sending unit wire it will read full. So sounds like maybe the wire is grounded out somewhere. You might try a external wire from the sending unit to the gauge and see if it reads ok then. You should also be able to test the sending unit out of the car by grounding the unit and move the float back and forth to see if the gauge moves.
 

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If you ground the sending unit wire it will read full. So sounds like maybe the wire is grounded out somewhere. You might try a external wire from the sending unit to the gauge and see if it reads ok then. You should also be able to test the sending unit out of the car by grounding the unit and move the float back and forth to see if the gauge moves.
+1 I'd unhook the wire from the sender, turn the key on, and check the gauge. Should read empty. Then clip the wire end to a good ground with a jumper temporarily. Gauge should read way past full. If so then the gauge, dash voltage regulator and wiring are all okay. Could also test the sending unit off the tank by making a long test lead that would let you operate it from in the cabin while watching the gauge. You'd have to ground the body of the sender while doing so.

Pat
 

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Did you test the sending unit before installing. Hookup a multimeter to the unit and measure the resistance as you move the float arm up and down. Then verify it matches the specs for your gauge (car). I installed a new tank in my 51 F1 and purchased a new sending unit (made in China). I checked the resistance and it was all over the place (I should have returned it then 🙄). It was never accurate, so I opened the sending unit up and found minimal, very thin wiring, not spaced properly. A miracle it worked at all. Bought a second one made in Tiawan and it’s been spot on for over a year. Much more robust construction. Make sure you ground the sending unit.
 

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+1 I'd unhook the wire from the sender, turn the key on, and check the gauge. Should read empty. Then clip the wire end to a good ground with a jumper temporarily. Gauge should read way past full. If so then the gauge, dash voltage regulator and wiring are all okay. Could also test the sending unit off the tank by making a long test lead that would let you operate it from in the cabin while watching the gauge. You'd have to ground the body of the sender while doing so.

Pat
I'm going to check this to see what I get. Thanks!
 
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