Originally Posted by Pleiades

The fuel level sender on the Z is basically a potentiometer, one side is earthed and the other side (green wire) receives a current fed from the battery via the instrument panel. The fuel gauge in the instrument panel is effectively just a voltmeter. The number of bars shown reflects the changing voltage as the resistance in the circuit is altered by the fuel sender potentiometer. Almost all fuel gauges work in the same way, so it�s should be feasible to rig something up.

What you�d have to work out first is the range of resistances produced by the sender across the range of float positions. There is no test given (or resistances) for the fuel sender in the workshop manual, but they�d be easy to work out with a multimeter either with the fuel pump assembly removed from the tank, or by leaving it in position and filling the tank 1 litre at a time from empty. Measure between the green and black wire's terminals on the sender connector on the fuel pump assembly.

You could then try and find a gauge that works within that range which might be a bit tricky (?), or get a cheap LED or LCD voltmeter and use the displayed voltage to indicate how full the tank is. The voltmeter option would probably be the simplest and neatest way to read fuel level. They are really cheap to get on ebay (something like this) and are small enough to mount in a variety of positions. It would give you a number (the voltage) which you could calibrate against the fuel level. On a lot of them the display turns off below a minimum voltage, which would/could give you a good low fuel level warning or indication of reserve.

Not sure which way the fuel sender pot works on the Z, but more often than not fuel senders have no (or minimum) resistance when the tank�s full and resistance increases as it empties. Based on that assumption, you�d get 12-14V (depending on engine running or not) when the tank was full and it would drop to whatever voltage the pot�s resistance will allow when the tank was empty. If you wanted to have a precise/constant full reading (that didn�t vary with charging voltage) you could easily fit a cheap voltage regulator/limiter to the supply to the meter so that the maximum voltage it receives from the battery would be 12.5V at 0 resistance.

If you didn�t want a numerical display, you can also get LED bar type voltmeters that are quite small, which would make an ideal fuel gauge.

Hope this gives you some inspiration, ideas and a few things to try�