Yamaha Analog Fuel gauages not working

[Jack1747]

I acquired a Argo-m2-21. The previous owner had twin f70s installed. The Argo has 2, separate, 35 gallon tanks. The boat has a fuel gauge for each tank. After a couple shake down rides it was apparent that the fuel gauges were on full all the time. With ignition switches off, gauges empty. With switches on, gauges full. First thing I did was to disconnect wire at sender. Gauge went to empty. Shorted the wires together at sender, gauge went passed full. Looks like wires are good and gauge is working. ??? Pulled sender from tank. Ohm meter swings from 38 ohms (full) to 238 ohms (empty). Both port and starboard tanks/gauges act the same. Since the boat is new to me I don't know if they ever worked correctly. Any thoughts? Short of running all new wiring....

[99yam40]

I would check to see if the gauges are set properly or even if the proper sending units for the gauges

[fairdeal]

With ignition switches off, gauges empty. With switches on, gauges full. First thing I did was to disconnect wire at sender. Gauge went to empty. Shorted the wires together at sender, gauge went passed full...
Pulled sender from tank. Ohm meter swings from 38 ohms (full) to 238 ohms (empty)

Then the gauge is working properly for an ABYC ("USA")
and there is no short or break in the wiring.

Although you report that the sender functions properly as ABYC type when removed from the tank,
nonetheless,

if "With switches on, gauges full"
but
"disconnect wire at sender. Gauge went to empty"

then the sender must be constantly exhibiting low resistance when installed in the tank.

I don't have any idea "why or how"
but that's the logical conclusion

[Jack1747]

Then the gauge is working properly for an ABYC ("USA")
and there is no short or break in the wiring.

Although you report that the sender functions properly as ABYC type when removed from the tank,
nonetheless,

if "With switches on, gauges full"
but
"disconnect wire at sender. Gauge went to empty"

then the sender must be constantly exhibiting low resistance when installed in the tank.

I don't have any idea "why or how"
but that's the logical conclusion

I agree. Next trip to the boat I will figure out whats wrong. What is baffling me is that two separate tanks/gauge/sender are doing the same thing. I have no way of knowing if this setup ever worked correctly. My guess is they didn't work since the engines and equipment were installed. The Argo was a bare bones hull when it went to the Yamaha dealer to be outfitted. The gauges are going to difficult to get to. I was hoping some one might have an idea about a common denominator.

[Jack1747]

Corrosion under insulation washers! Constant 50 ohms when grounded.DSC_0062.jpg

[Jack1747]

Not fixed. Finally got down to the boat. Reinstalled sender to boat wiring but not in tank. Same issue. The sender works on the bench. When hooked to boat wiring gauge goes to full. I was sure it was going to be fixed I didn't take my multi-meter.

[77tarheel]

Check continuity between ground on gauge and ground of battery and also continuity of positive side of inputs. On my Carolina Skiff, these gauges are wired to each other in series. Good luck

[Jack1747]

Check continuity between ground on gauge and ground of battery and also continuity of positive side of inputs. On my Carolina Skiff, these gauges are wired to each other in series. Good luck

I wish I knew if this ever worked right. Now have to approach it as a installation error by the Yamaha dealer. Since its 2 gauges, 2 tanks, 2 senders, 2 motors, I am leaning toward a grounding issue. This Argo M2 has a weird battery system. 2 batteries under the console wired to a switch. From the switch to the transom are only 1 set of battery cables. At the transom there is a box where those wire breakout to the twin engines. Not sure where all the common bonding is. Going to have to start there.