Good deal Jay and glad we were able to help. I've gotten a bunch of good info on this site from a lot of good people including you.

Mods. This needs to be a sticky!

Yes! I have the same issue with mine, however slightly different.
 

Yes! I have the same issue with my 68's fuel sending unit.

I am pleased that I have resolved all of my electrical issues of the car. . . . . except for this one. Put in the cluster and the fuel gauge needle was near empty, then turned the key to the accessory position and the needle has disappeared past the Full indicator and has stayed there since.

My attempts:

• Pulled the feeder wire to the unit and made a loop off of the battery = good, quick and bright - no break in the wire.

• Media blasted the insides of the tank straps, related hardware and filed trunk support hangers for clean metal.

• Sanded sending unit's eyelet grounding spot at trunk.

• Used a screwdriver probe with an internal light to check the harness at the back of the car with ground to the bumper. It took about a second to light and the bulb was quite dim versus my other points of contact.

• Pulled the harness at the dashboard clip and probed there, still the same dimness. Not getting enough voltage?

• Polished the printed circuit and needle gauge screw threads at the back of the cluster with 0000 steel wool.

• Media blasted a spare 90 ohm sending unit, (resistance stamped into the armature cover), and have tested with an Ohm meter. . . the reading is everywhere! I have not swapped the current unit in the tank for this one yet.

Not sure what else it could be?

Thanks for the thoughts and insight
Alex

Pull the pinch fastener on bottom side of the sending unit off carefully with a small pocket screwdrive...slowly. You can reuse it. Under that is where your ohm's are losing contact and jumping around. Rust..oxidation and just crap build up under there. It will come out as a dust.. careful with the rubber washer as well.

Reassemble and check the ohms again and see if you did some good.

Good Luck.

Use 1qikta's jumper method to test sending unit (1st pic in post 26). Good thinking 1qikta!



Charles

I think I'd narrow down the search first.

Unplug the body/ribbon harness in the trunk.
(1) Ground the tan sending unit wire, going up front to the guage, and see if the guage drops back to empty.
(2) Check sending unit wire from tank to ground, with an ohm meter, and see if the sending unit is in the 0~90 ohm operating range.

With this info you'll know what direction to head in, up front or underneath.

FUEL SENDING Unit issue resolved!
 

Want to pass along a sincere thanks to those who provided their insight on the matter! Fuel sending unit issue resolved!

Details:
First, removed the push-on retainer cap and cleaned this along with the brass contact pin of the sending unit. Next, grounded the sending unit harness to the bumper, turned the key to the accessory position and within a ten second count, the needle reappeared and had rested at empty. Drop the tank, remove the existing sending unit and replaced with spare. Grind trunk supports for clean metal to make contact with topside of tank. Grind a bare metal spot for sending unit ground. Disconnect harness plug at trunk and turn key, needle began to rise back to full, shut off key, re-connect and test. . . .works!

Main task to consider before giving up or paying someone else to to this - clean all points of contact and remove all rust to ensure a good ground. This is, if not all, the majority of electrical problems this era of cars have. When I started, only a quarter of my electrical system worked. It was all there with no rewiring foolery. Went through and pulled all of the blade connectors and polished. As I progressed each section of the electrical was returning.

Hint:
Repressing retainer cap onto brass pin - used a small quarter inch drive ratchet socket on a screw driver

Don't it feel good?
Good deal.

Glad it's working, but......
 

Curious about all the media blasting, cleaning points of tank to body contact, and bare metal.

Tanks usually have something to insulate them from the body. Tar strips on top or something.

IMO Sending unit ring should have a ground wire to the body to complete the circuit. Not tank to body contact.

Just worried about rubbing, rust, and noises. Stuff that might lead to premature tank failure.

Just concerned a little bit

I agree with above, wholeheartedly.

FUEL SENDING Unit and bare metal contact
 

Understandable the concern, re thought this since reading.

The tar pad broke in to several pieces. In my stash of packaging materials I found a roll of thin closed cell foam with a blue liner backing, probably 3/16" to 1/4" thick, quite dense and durable, (this is used to wrap new car bumpers and some body panels). Dropped the tank again, measured the tar pad dimensions onto the foam and cut to size. Reinstall. Kept the harness unplugged while the key was in the accessory position to get the gauge needle back to full, replug and . . . A-Ok! So yeah, a detailed cleaning the sending unit was needed. That was the last test to confirm that the sending unit was functional. Tank is secure and padded from the under body.

Alex

I was able to diagnose my fuel gauge problem as the sending unit this evening based on recommendations here. Tomorrow I will take on the repair..

lazlo, I like that standard hub cap look on your car, very well done!

Also, glad to know the question helped.

Thanks,
Alex

Thanks, I ran rally II's the first two years & changed it out this spring. I am surprised at the number of positive comments the car has got since I put the dog dishes on.

The answer to this question is probably obvious but I need to ask it anyway. Currently when the tank is empty the gauge shows half full. I already checked the fuel gauge & it works. To calibrate the sending unit is it just a matter of bending the float up or down? & in this case I would want to bend it up to get more travel... correct?

My thinking is still kinda cloudy this morning but it seems to me that if your tank is empty, the float is all the way down. No bending is going to change that. Sounds like it may have the wrong resistance or a bad ground. You need a good ground to get the empty reading.
Now, if the tank was full...and it read halfway...AND the movement of the arm was only half up as in, hitting the top of the tank, then yeah, you could bend it down to get more travel.

There is a wire that runs off the top of the tank and grounds on the bottom of the trunk, at the back of the tank. Do I just need to clean that real well or is there other ground I need to address

If that ground is good, that's sufficient. You have an ohm meter? If not, just make sure it's really grounded well.

I was getting ready to ask the same original question about my fuel gauge, and then I found this thread. I read through all of the posts, and I think I understand where my car stands. It is a '68 Lemans. Over the last few months, I installed a new engine and rebuilt trans. I painted the underneath side of the car with the engine and trans out. I removed the gas tank and cleaned it out. I had to install a new strainer on the fuel sending unit, because the old one fell apart in my hand when I touched it. I cleaned and reinstalled the sending unit, painted the tank and put it back on the car. I reused the thick tar paper mat on top of the tank. The first time I started the car, the fuel gauge was showing around 3/4 full (that's probably about how much gas is in the car). The next time I started it, the needle was nowhere to be found. I assumed it was past full, but could not see it. I took the tan sending wire off of the connector where the license plate light also connects. I then grounded the tan connector wire, and the needle dropped to empty. When I took the temporary ground wire off, the needle slowly went back to past full. From this thread, I think this means that the gauge is good, but the sending unit is bad. Please let me know if I am stating this correctly, as there is a ton of info in this thread. Thanks.

Either it's bad or you have a bad connection to, or integral to the sending unit. I can't remember without going through the entire thread again...but I think that's what Jay had. Like a bad crimp connection or contact integral to the sending unit.