mkh

Ok I have a rebuilt fuel gauge, a new gas tank and a new gas tank sending unit. With the key off the gauge reads empty. With the key on the gauge reads full. ( I know the tank is only half full). I can run a jumper wire from the brown sending unit wire at the back of the gauge to a known ground and the gauge goes to empty. What could be the problem? Is there a way to bench test the sending unit? Thanks for any help as this one is driving me crazy and getting very expensive. (I removed the fuel gauge so many times I damaged the temp gauge that was working fine and 190.00 dollars later it is back working) Mike

MasterDave

If you installed your float directly forward in the tank it will hit the inside wall at the 1/2 mark. The float needs to be at enough of an angle, maybe 45 deg so it will have full range of movement. Don't ask me how I know this.

mkh

Thanks Dave. I noticed that when I was installing it so it is ok. any other ideas how to bench test the sending unit? Thanks

0Willcox Corvette

The gauge works off ground, ohms and power. Since the gauge is moving with the key you have power and ground, so this only leaves ohms as the problem. The two post on the back of the gauge are power and ohms and the gauge picks up the ground from housing when installed.

Go to the tank unit and see what the ohm's output is where the brown wire is attached. I'm not positive and it's been a very long time, without checking I think full is 32 ohms and empty is zero. Someone post if this is wrong..

The indication to me is that the you are missing ohms input since most gauges will peg full without any input. Either there is a break in the wire, the sending unit is not grounded or the sender is defective.

If the ohms wire was grounded out, the gauge would read empty! So if you go to the tank and ground out the ohms wire you should be able to see the gauge go to empty.. thus testing gauge function.

Verify that the sending unit is getting a good ground.

Willcox

mkh

Thanks for the help guys. How do I test the ohms at the sender unit. I have it out of the car at this time. I have a ohms tester but how do you hook it up to verify o to 32 ohms? Mike

0Willcox Corvette

Set it to the ohms setting and put one side to ground, the other to the post on the sending unit.

Then you should be able to move the float up and down and see a change.

I did a help and repair page on our site for mid year, 68-76 and 77-82 but I've never done one for the c1 cars... Yet..

However, if you go to this page.. you'll see exactly how to test the sending unit.
http://willcoxcorvette.com/repairand...lp.php?hID=276

Also just a note.. seems that the cars (c1) had a grounding problem on the fuel sending unit circuit. If I remember correctly I ran an extra ground from the sending unit to the frame on my 62.

Willcox

mkh

OK, I am holding the sender unit in my hand hooked up to the multimeter. The red wire goes to the stud and the black wire goes to the round part of the sending unit where it is secured to the tank. My reading is 1 and will not move. Does this mean the sending unit is bad. I have it hooked up the way you show it in the pictures. Mike

joshtried

either you have an open circuit or your sending unit is bad, though i think you should have the unit grounded in the car? and the power hooked up too?

MasterDave

That is the correct hookup, if you move the float full range and you get no reading you need a new sending unit. You have an aftermarket unit there, make sure the wire has continuity also.

0Willcox Corvette

Yes 1 = open circuit..

Looks like the sending unit may be defective.

Willcox

mkh

Hi I checked for contunity and when I test the wire at the half circle area I get no light, but further up the wire I do. Wow I have learned a lot about fuel gauges. The sending unit is brand new and looks like it is bad. I thought i was doing everything correct but just didnt want to believe a new sending unit would be bad. Oh well order another tomorrow. Thanks for all the help. Mike