1988 Chevrolet Cheyenne

On a 1988 chevy truck how can I check the fule sending unit I have changed the relays but the fule gauge still noy working
July 8, 2012.

The arm that floats with the level of the gas may be stuck. You will have to access the panel by fropping the tank and the sender is in the front middle. Check the float arm to see if it is stuck.

The arm that the float is on is not stuck if the sending unit is bad cant that make the gauge not work cause it will not go back down it stays between 3/4 and full

Jul 8, 2012.
Yes it can. Of course the gauge itself could be bad but that is last resort.
You might try getting the trouble codes pulled as that will show electrical problems. Any Advance Auto or Auto Zone will do this for free. You don't have to have a check engine light on to have trouble codes.