1963 Issues With Fuel Gauge Reading

Bill –
The fuel gauge on my 63 Sedan was inop. I ordered a new fuel tank sending unit from Lincoln Land. When I installed the new sending unit it only reads 3/4 or slightly less, when the tank is full. I also replaced the constant voltage regulator. The service manual says to substitute a known good unit to verify the problem. Since I only have one unit, that is not possible. When I ground the sending unit wire to the body of the car the gauge goes past full. I pulled the sending unit back out and measured the resistance. When the float is moved to the full up position as would be a full tank of gas it reads 5 ohms from the terminal to the body of the unit. My question is, will you take a known good sending unit and measure the ohms of the unit when the float is moved to the full position? This would help me troubleshoot the problem Before the old sending unit wore out it would read full when appropriate.
Thanks,
Jeffrey
—————————————————————————————————————-
Hello Jeffrey –
Some of these electrical problems can be frustrating. We can check our Sending Units here at Lincoln Land but there is another way to test your new sending unit first. Remove the new unit from the tank, plug the wire from the dash gauge in to that tank unit and ground the body of the tank unit. Turn the ignition on a then operate the tank unit by hand from empty to full. Observe the dash gauge to see if it now can reach the FULL and EMPTY mark during the test. If it cannot read full at this time, the sending unit is faulty or its rod is bent or the float is defective. Another possibility is that the constant voltage regulator in the dash is defective. With the key in the on position probe the sending unit wire at the gas tank. This cvr sends out a flashing or pulsating signal to the tank unit. If this signal is not clearly observed at the fuel tank wire the cvr could be defective. Do not directly ground out the cvr wire as a test as this could be detrimental to the gauge. Please be very careful while working near the open fuel tank in order to avoid a fire. Let us know what you find.
If you have any further questions or do not fully understand the above suggestions regarding diagnosis please do not hesitate to call Lincoln Land and ask for George. He will get one of our techs to discuss the matter with you. Together we will get it working properly as this is a common issue with gauges.
Sincerely,
Bill