I've been setting up my gas tank with a fuel return line from the pressure regulator and decided to match up the level shown on the dash with the actual amount of fuel in the tank. I'm running the larger 12.5 gallon tank and had bent the float arm so it would reach the bottom of the tank. My VDO (Porsche 914) combo gauge usually showed full most of the time, dropped to a little above 1/4 and then dove below 'R.'
When I was finished with the tank work, I put two gallons of fuel back in and then put a 1k potentiometer between the gauge wire on the tank and the sender. Turning the potentiometer until the gauge read right at the beginning of 'R' and then checking how many ohms the potentiometer was providing at that position gave me the value of the resistor I needed to add to calibrate the gauge. Turns out it was 25 ohms in my case. I only had 22 ohms or 33 ohms 1/4 watt resistors on hand so I put the 22 ohms in line with the connector to the tank sender. I added a short piece of non-connected wire alongside to strengthen that section and then covered it with heat shrink.
Now it's 'right' or at least close enough!
