Chevrolet Repair: gas tank sending unit, gas tank sending unit, 68 chevelle

Question
I have a 63 Impala that gas gauge does not work(shows empty)
if I take the power wire off it shows full,is there a way to check without taking tank out.

                     thanks ron bryson

Answer
Hi Ronald Bryson,

Nice car.  I almost bought a '64 convertible in 1985, when I was buying my first car.  It was in need of much.  I bought a convertible '68 Chevelle instead.  Wish I still had that.

Anyway, enough about that.  You could take readings, but you need to raise and lower the level in the tank to see if it is trying to send a signal.  You would look at resistance.  Chances are the sending unit is bad.  When you unplug the power, the guage reads full because that is unresisted power.  You have + - and variable resistance.  When you unplug the power, the resistance is zero.  

Now is the sending unit burned out?  Or is the floater not floating?  That is the question.  It is best to pull the tank, pull the unit, then take readings for resistance as you operate the float.  If no change, the unit is bad.  

C J S