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I have a 99 ultra classic, 22,000 miles. One day my fuel gauge started bouncing around. Obviously the float bounces up and down when the bike is moving but now it is reflected in the fuel gauge. Give it gas the fuel gauge goes to half, hit the brakes it slams to full sit at a light and don't move. The gauge reads correctly. Is it the fuel sending unit, loose ground?
 

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I have a 99 ultra classic, 22,000 miles. One day my fuel gauge started bouncing around. Obviously the float bounces up and down when the bike is moving but now it is reflected in the fuel gauge. Give it gas the fuel gauge goes to half, hit the brakes it slams to full sit at a light and don't move. The gauge reads correctly. Is it the fuel sending unit, loose ground?
It is likely the gauge itself. It can be tested easily.You just have to remove the outer fairing.

Looking at the back of gauge there are three blades. The vertical blade on the left-hand side is 12V+ switched. The center horizontal blade is the ground and the vertical blade on the right-hand side is the variable voltage from the sending unit.

Temporarily disconnect the gauge. Using jumper wires or whatever you have, connect a 12V+ to its correct (left-hand vertical) blade and a ground to its correct blade. No wire to the sending unit blade. In this state, the gauge should read empty. (you can also pop those two needed wires out of the connector and just plug them into the gauge if you understand how they come out)

Now for the test: Apply 12V+ to the sending unit blade. (You can just jump across from the other blade) When you apply the voltage, watch the gauge. It should slowly and steadily sweep up to full.

If it jumps to full very quickly - almost instantly - the dampening capacitors in the gauge are shot and the gauge needs to be replaced. If it sweeps slowly and steadily, it's fine and it's another issue - probably the sending unit.
 
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