I installed a VDO gauge and sending unit in a car. Below is a link to the type of sender I used. It has to be adjusted correctly for the depth of tank by moving the rheostat up and down and changing the length of the float arm. It's not difficult.

Sending unit

Sounds like the best option for you is to empty the tank and drop it so you can get at it. Remove the sender and confirm that it is set up so that it works across the range.

Last edited by Gord&Fran; 11/30/2017 12:25 AM.

Gord 🇨🇦
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1954 1/2 ton 235 4 speed