The sensing system is located in the fuel tank and consists of a float—usually made of foam and connected to an actuating metal rod—attached to a variable resistor. When the float moves due to changing fuel levels, the wiper moves across the resistor, causing a change in voltage.

A fuel gauge displays that fluctuates between empty and full may be due to a mechanical failure. The fuel sending unit float arm may ‘stick’ at certain levels, and fall back into place either naturally or with help from vehicle movement. Once the float arm falls back into place, the fuel gauge becomes accurate again.

The fuse box will either be located under the driver’s side dash or in the engine compartment, so consult your owners manual to pinpoint the location so you can replace the fuse.

The gauge is provided a certain amount of voltage from the fuel sender. The gauge will uses this voltage to know where to move the needle on the gauge. Jumping the 12 VDC power to the sending unit, the gauge should shoot straight to completely full. If we remove the sending wire and the gauge stays full.

The usual problems are a blocked orifice (little hole in the arm), a blocked vinyl tube and a disconnected, broken, cracked or holed vinyl tube. The easy way to check if to remove the tube from the pitot tube mount and blow into the vinyl hose. If the speedo moves, it’s likely the pitot is plugged.

Make sure you have power going to the tach (usually fed by the keyswitch – purple wire). Make sure the “signal” wire is connected (grey wire). Make sure the Tach has a connected ground wire (black wire). Make sure the Tach is set to the correct number of poles (if it’s an aftermarket/multi-model tach).