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post #6 of Old 05-14-2013
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Re: Fuel gauge reads empty

Put a meter across the connections and with the engine switch on (ignore the alarms) you should read some value of over 12v - the same at the back of the gauge as on the tank.
If you get that it's not the gauge, the wire or the connections. Pull the sender and replace (varying cost from 29 bucks to 100+).
If you have power at the tank but not at the gauge you'll have to check the gauge via resistance check (meter on ohm's and a connection to each end of the wire). You should read a small amount of resistance. Infinite resistance indicates an open circuit, bad gauge. You can always check a meter's resistance/ohm reading by simply touching the red to the black - that's what good wire looks like. Then touch both to a working light bulb (connector on the base and other on the socket), that's what a working circuit with resistance works like. Everything that uses (consumes) electricity has some measure of resistance.

Then check the wires the same way (a long extension will be needed for your meter). Ditto, a small amount of resistance indicates the wires are good, infinite resistance means air gap, i.e. open or broken wire.

If you don't have power across the connections at the tank you'll have to check the other (source) end of the wires to make sure there is 12v there (usually 12v is provided from the engine harness - a take off from the alt since you only need fuel levels when the engine is running). You'll have to trace that out as each boat installation is different.
Once you think you have the right wires do a resistance check as described above just to be sure.

If you don't have a meter, when you get one (not if, when) get a digital one. Analog meters are not sensitive enough. Buy a spool of 20 feet of cheap wire and some small alligator clips too so you can make extensions.
Do voltage checks with the ignition switch on (or running if the alarms get to you). Do resistance checks with the ignition off.

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