Is it grounded well, or plugged in backwards?

 

I will check have had many grounding issues
How could it be plugged in back wards? If I remember correctly there is just a single slide on plug on the tank

sof2424 it is the original sending unit

arden12 I will try unplugging it good idea I bought the car a little over a year ago and dont remember looking at the gauge but Im sure I would have noticed it being full I only drove it about 20 feet

 

If you installed a new fuel sending unit in the fuel tank make sure that the Ohms on the sending unit and the gauge match. I just order new Autometer gauges and had to match my gauge and Scott Drake fuel sending unit. The Ohms should be 10 Ohm Full and roughly 78 Empty.

 

If you connect the wire to the sending unit directly to ground the gauge should read Full. With the wire disconnected the gauge should read Empty.

 

So if this is the case then the sending unit in the tank must be bad because when I pull the plug off the tank the gauge goes to empty when I plug it back in it goes to full am I correct with my assumption?

 

Sir, You have a grounding problem.

)


Tony K.

 

I would think that the grounding strap on the sending unit has some type of connection issue. A replacement sending unit usually makes the fix..

)

Tony K.

 

Or....you could have a break or rub through somewhere along your sending wire. If you ground out the wire - anywhere along wire - it will peg out full on the gauge.

There is a few obvious ways to test this, with continuity or with a temporary replacement wire, but first get a good flashlight and trace the wire, and inspect it.

I have had my issues with a 70 and a 69, but one thing that surprised me is the way the original stuff keeps working. Check the obvious things first, before removing the dash.

Also, if the PO has put some sort of sealer around the gas tank to trunk floor seam, it can disrupt the grounding. try a good ground cable temporarily from sender to body. Might be a simple fix.

 

Gauge goes to empty when the wire is disconnected so the short-to-ground is in the sender. High resistance is at the EMPTY end of the gauge so if there's a poor ground between the sender and tank or tank and chassis the gauge will stay on the low end.

 

Bartl, I just went back through my post on my gauge problems and one of the tests I conducted was to ground the sending wire and switch the car ON, and all of the gauges went to high.
Is it possible a rubbed through wire along the path of the sending wire from the fuel tank is grounding on the frame? Wouldn't that do the same thing as grounding the sending wire? And causing the gauge to go to high?
This is confusing me now. Would a rubbed through wire on the frame cause low resistance or high resistance? If I grounded out the sending wire on the frame and the gauge shows top peg, then it must be zero or near-zero resistance, right,?

 

It would do everything but let the gauge go back to zero when you unplug the sending unit.

 

It sounds to me like the tank may have a bad ground because when I unplug the wire the gauge moves to empty this will rule out a shorted wire along the way
I will try and run a ground strap to the tank if that does not help then It must be the sending unit are they hard to remove?

 

If you had a bad ground the gauge would never come off empty.

NO RESISTANCE means a complete circuit.....to ground...and a gauge on full.
The HIGHER the RESISTANCE in the circuit, including an OPEN CIRCUIT which is INFINITE resistance, the lower the gauge reading.

The sending units aren't that hard to change, just a little awkward sometimes. The fuel must be drained from the tank, you use a brass drift and a hammer to drive the locking ring off and remove the sender. There is a rubber o-ring gasket to replace that I use Vaseline to hold in place while I secure the new sender with a new locking ring. I always test the sender OUT OF THE TANK using a jumper wire to provide a good ground, before installing to make sure it reads correctly. Sometimes you need to bend the float arm. You want it to read empty before you run out of gas.... :lol:

 

Start by looking at the wire, a pinched wire will be shorted to ground and will act this way.

 

Again, if you disconnect the wire from the sending unit the gauge will stay full if the wire is pinched or shorted to ground.