63 fuel gauge reads full all the time.

[Bearcamp]

As soon as I turn the key on the needle goes from empty to full. Here's what I checked. I had no power to the sending unit and found the wire was unplugged from the fuse box. Connected it and now I have 12 volt at the sending unit. I checked for power at the gauge and I have 12 volt there also. Checked for ground at the sending unit and gauge and I have ground at both. Now what next? I'm thinking that either the gauge or sending unit might be bad. Maybe I'll pull the unit from the tank next.

[Bearcamp]

Found out that the wire that was hanging under the fuse box shouldn't be hot. Is that right? The wire that has a plug end on it is just hanging under the fuse box and not connected. But the other end goes the the center of the sending unit. I need to find out where it plugs into. I need a wiring scimatic.

[mark 66]

There should not be anything energized going to your fuel tank unless, you have fuel inj. pump. check wiring from tank to see if it is grounding out to the body somewhere. should oly be 1 wire coming form tank to guage and the other wire close to the sender is grounded to the body. guage works on ohms resisitance not voltage.

[Bearcamp]

There is a ground wire going from the tank to the body. Another wire on center of unit with a 3/8 nut that is brown. It goes to beneath the fuse box and has a connector end on it. So I connected a wire to that end and slid it in the plug at the sending unit (brown wire) and still read full. I need to find out where the brown wire from the sending unit goes. I did see it goes into a taped up harness by the column but can't fint it after that.

[61_FL_Apache]

Pull the sending unit out of the tank. Reconnected it and turn the key on. Move the arm back and forth and see if the needle moves.

[ABX131]

There should be a hot wire (switched with the ignition) that goes to the left side of the fuel guage, the right side wire from the guage goes to the fuel tank sending unit. There is also a grounding tab on the sending unit that goes to the body. I have the same year and the very same problem. I believe my sending unit is bad and needs to be replaced. 63's have a 30 ohm sending unit so if you replace yours make sure you get a 30 ohm, not the 90 ohm for later years.

[par4tom]

When you say the left side wire, is that the left side as you look at the gauge?
Posted via Mobile Device

[luvbowties]

Originally Posted by Bearcamp

As soon as I turn the key on the needle goes from empty to full. Here's what I checked. I had no power to the sending unit and found the wire was unplugged from the fuse box. Connected it and now I have 12 volt at the sending unit. I checked for power at the gauge and I have 12 volt there also. Checked for ground at the sending unit and gauge and I have ground at both. Now what next? I'm thinking that either the gauge or sending unit might be bad. Maybe I'll pull the unit from the tank next.

Look at this PLUS at file coming via PM for testing.
sam

[luvbowties]

Originally Posted by Bearcamp

There is a ground wire going from the tank to the body. Another wire on center of unit with a 3/8 nut that is brown. It goes to beneath the fuse box and has a connector end on it. So I connected a wire to that end and slid it in the plug at the sending unit (brown wire) and still read full. I need to find out where the brown wire from the sending unit goes. I did see it goes into a taped up harness by the column but can't fint it after that.

"I need to find out where the brown wire from the sending unit goes."
It goes under mats & eventually to fuel gauge's "TANK" or "SENDER" terminal--the one closest to passenger's side. Ensure the other gauge terminal has voltage applied (probably via a spade terminal on fuse box that reads FUEL).
HTH'
sam

[luvbowties]

Originally Posted by par4tom

When you say the left side wire, is that the left side as you look at the gauge?
Posted via Mobile Device

Sorry, just now saw you are the one asking for help. Yes, as you look at the gauge from the driver's seat....the one closest to driver's side of cab.
sam

[ABX131]

I am dealing with this same problem and I am sure it is my sending unit. Unfortunately due to bad weather and no time I have not made any progress on this topic or any others.

[par4tom]

That's what I thought. Thanks for a great post.

This fuel gauge is basically and in-line impedence meter, with the needle moving based upon the amount of resistance in the sending unit. More accurately, the amount of amperage it can send back to ground throught he sending unit.

Beautiful!