Fuel gauge/sender ground fault?

[royholleman]

Trying to determine the cause of my fuel gauges going to full and staying there when key is turned on. Checked ohms at the tank and seems correct. Checked ohms at fuel gauge before turning key switch on which matches reading at the tanks. Once key is turned on gauges jump to full, although I know the levels are around half in the tank. Trying to determine if this is a ground fault and if so determine if the ground fault is at the tanks or gauges. 3 tanks, diesel. All three gauges share a ground with other gauges that are working correctly.

If a ground fault at the senders how to track this down. Odd that all three gauges are doing the same thing 2 tanks are in the engine room, port and stbd, one is under the aft berth.

Performed a continuity test on one tank from neg terminal on sender to bus block/bar and get a positive continuity signal on several connectors. Trying to go back to high school electronics class, but that was 49 years ago and just can’t recall how to full track a ground fault, if this truly my issue.

Suggestions welcome,
RH

 

[diver dave]

That is odd. They go like this: dc power>gauge>variable resistor(sender)>ground

A too full reading tells me too much current, too little sender resistance. Or, 12V is very high or NEG is below zero volts.
And multiple instances. Is 12v ships power normal?
Any idea if senders are N America or Euro standard?
Do you have a rather rare voltage regulator, like many cars? OOC reg at full tilt will give high readings.

 

[royholleman]

Will check voltage when getting back to the boat. I did a voltage check on a chart plotter also located on the flybridge and got a reading of 13.6 volts. Will check at the gauge, but the fuel gauges share not only a common ground with other gauges but also power, with the other gauges working fine (temp, oil pressure, etc). Senders appear to be N American and did work for a number of years. Thank you

 

[diver dave]

Will check voltage when getting back to the boat. I did a voltage check on a chart plotter also located on the flybridge and got a reading of 13.6 volts. Will check at the gauge, but the fuel gauges share not only a common ground with other gauges but also power, with the other gauges working fine (temp, oil pressure, etc). Senders appear to be N American and did work for a number of years. Thank you

The ground on a fuel gage is typically just for the backlight. Its the sender that has one side grounded, at the tank. Do the tanks share a ground wire? Is bonding involved? Is there an active anti galvanic system?

 

[4fun1]

Could it be like older car guages, when you turned the ignition on the guages would go to full then read normal? Not sure how they were wired or worked but maybe something in your key switch.

 

[royholleman]

Tanks are grounded and from what I remember yes on the active galvanic system. Will remove and clean green wire (grounding system) from each tank, clean and make sure they are making good contact. The black negative on the tank sender has been removed, cleaned and making good contact. When I check continuity I get a strong signal from the negative wire going to the sender to the bus bar, however the signal is heard from touching multiple wires along the bus bar.

 

[royholleman]

when key switch is activated the gauges jump to full and stay there. I have taken the sender and ground wires off and jumped those two with a 110 ohm resister and the gauge reads about where it should so I assume the gauge is working properly. Think diver dave may be on to the root of the problem doing something in the grounding system.