Fuel gauge/sending unit problem 1969 Cadillac hearse

[juggalo78]

I am working on my 69 Cadillac hearse. The fuel gauge sending unit went bad and I'm replacing it. With the wires disconnected from the sending unit, the gauge reads "full". I strap the wired together and the gauge drops to "empty". The problem is that when I hook up the sending unit, and with the float all the way down, the gauge read "full" still. If I push the float up, the gauge drops to "empty". I've tried reversing the wired and polarity, but I get the same result. Please let me know if u have any ideas.. Thank you, Jeremy T.  Olathe, Ks

[The Tassie Devil(le)]

Sounds like the internal Rheostat is burnt out.

Here is what one looks like from the inside, once the cover is removed.

Bruce.

PS.   Sorry about the poor quality of the picture.

[J. Gomez]

I am working on my 69 Cadillac hearse. The fuel gauge sending unit went bad and I'm replacing it. With the wires disconnected from the sending unit, the gauge reads "full". I strap the wired together and the gauge drops to "empty". The problem is that when I hook up the sending unit, and with the float all the way down, the gauge read "full" still. If I push the float up, the gauge drops to "empty". I've tried reversing the wired and polarity, but I get the same result. Please let me know if u have any ideas.. Thank you, Jeremy T.  Olathe, Ks

Are you getting these reading with the new sending unit?? If you have an Ohm meter read the resistance on the new one, it should be zero (full) to 90 ohm (empty).  Your description indicated the sending unit is not the correct one as it is set in reversed. Changing the polarity at the gauge would have no affect to correct the problem.

[bcroe]

Actually, I think it should read 0 ohms empty and 90 ohms full.  I never heard of that problem before.  Bruce Roe CLC # 14630

[mario]

jeremy:
be sure that you ground the sending unit while testing.
ciao,
mario