I was having problems with my fuel gauge on my 1975 Scout II. It was only reading 1/4 when I knew the tank was full. Sometimes it would not read anything at all. My first thought was that I needed a new fuel sender. After replacing the fuel sender, It still was reading 1/4, when I knew it was full and often reading empty. So I thought that the gauge was bad, so I looked around and found a used gauge and swapped it. Same thing,… not reading correctly or not at all. Next I checked the circuit that measures the fuel level and that was about right.
After much hand ringing and thought, I focused on the voltage regulator. It is located on a seemingly unrelated gauge. On the back of the oil/temp gauge is a small electrical box, it supplies circuit protection and constant amount of voltage for all the gauges. if it is not putting out this “clean voltage” they may or may not display a reading. I could use a used regulator
New voltage regulator fixed my fuel gauge
but I decided against that because I might have the same problem again in a year or two. So I replaced it with a new model that fixed the problem. It really was easy to do and I did it myself. Now my gauge reads reliably but only to 3/4 when I know it is full. The last quarter turns out to be corrosion in my wiring harness and connectors. I am now working to clean all the contacts in my connectors to remove the tiny little bits of corrosion that are inhibiting continuity to give me a full reading.
It has been a long road but I will keep at it until it is perfect.