Your gauges are run by a not so accurate 5 volt supply. If you just reading a little low that is probably the problem. Most guys to fix this use a 5 volt regulated adjustable power supply. With the adjustment you can set it right on. The other issue is where it reads when it’s empty. Bullet Bob has a nice set up to help with that. The 5 volt supply is located behind the gauges. There was a post not long ago on here I think on how to make one, not hard, or you can probably buy one on e-bay.

First you need to be sure the float is not leaking.  It may be half-full of gas, making it not float to the top when the tank is full.

To check the gauge you don't really have to take anything apart.  Just unplug the sender from the wire.  Route a jumper wire from the removed sender wire to where you can reach it sitting in the driver seat.  Turn on the accessory position and note the gauge, wich should be reading zero.  Then momentarily hold the jumper wire to ground to see the gauge move.  Do not hold the wire continuously to ground, but just long enough to see if the gauge will read all the way to full.  If it does, you have eliminated the gauge as the problem.

Most new sending units are garbage.  The one I bought recently reads just above empty with nearly 8 gallons of known fuel in it.  It does read full when the tank is full though.  And this was AFTER I set it up using BB's template and instructions.

Mark Z wrote:

How can I/We get the diagram instructions on how to set up a new fuel sending unit? Mine is horrible. I need to either fix the low low fuel sender that I have, which cant be replaced or put a regular sender in and change the plug end at sender? Anyone ever do this? oh its a 68 with the low fuel warning

thanks

Send email to efi4u@bresnan.net and in a couple of weeks...when I return from the bash...I'll send you the inst. and templates.  I had good luck with this, which is why I wrote it,  but it sounds like MS did not.  I haven't gotten feedback from others yet so your results may vary.

Leaving now for the BASH.

Later,

BB & Jean
 

The following numbers are what the O/E sender should read.  The factory sender is non linear and most repops are linear will will give false readings.
If your sender matches these O/E nuimbers look for a bad gauge or IVR.

  10 ohms = Full
25 ohms = 1/2
50 ohms = Empty
73 ohms = Below Empty.

Hey, Bullet... Since I still had that email with the gauge attachments that you sent me, I forwarded it to Mark for you.  So he doesn't have to wait two weeks.