I'm not sure if I'm using the correct terminology here, but I think what I need is a resistance multiplier.
I have a situation with my vehicle that I think I can remedy with a (relatively) simple circuit, but I am not knowledgeable enough to work out how to do it.
My car actually has two fuel level sending units, one in each side of a saddle style tank.
Each sending unit is essentially a potentiometer with a max value of about 200 ohms and a min value of very close to 0 ohms. More ohms == less fuel in the tank, and 0 ohms means the tank is full.
They are wired in series.
There is a short in one of the units and it has no resistance, so the computer thinks this side of the tank is completely full. The other side works fine, and that is the side that has the electric fuel pump so that's the side that really matters anyway.
As a consequence, the fuel gauge reads about half empty when it is actually empty!! This is ok for me for now, and I can watch the mileage on the odometer to know when it needs fuel too, but I would really like to fix this up, esp if it's not too tough to do. The sending units are a lot of work to replace and very expensive, and junk yards don't seem to keep the one that I need, keeping only the 'electric pump' side.
What I'd really like to do is have a circuit of some kind that effectively doubles the resistance of the one sending unit that does work so that completely full is still 0 ohms, but completely empty would be 400 ohms rather than 200 ohms. This way the fuel gauge would read completely full or completely empty based on only the one sending unit. There is an ejector pump that pumps fuel from the other side of the saddle tank, so the levels should be relatively close anyway, and also, as I said before, the electric pump is the one that needs the fuel anyway so in the end I really only care about what's on the side with the working sending unit.
Anyway, I'm sure this is possible, but I'm not sure how to do it, so I put it to the board.