Fuel Gauge Replacement - Ohms?

[mhinnc]

The original fuel gauge on our '72 C&C 30 MkI has finally met its end. To match a replacement with the sender, would I not just ensure the tank is filled and check the Ohms across the sending unit leads? The tank is newer than the boat, replaced by another previous owner, and so I'm pretty sure the sending unit isn't original. Any insights? Thanks!

[joe_db]

The original fuel gauge on our '72 C&C 30 MkI has finally met its end. To match a replacement with the sender, would I not just ensure the tank is filled and check the Ohms across the sending unit leads? The tank is newer than the boat, replaced by another previous owner, and so I'm pretty sure the sending unit isn't original. Any insights? Thanks!

99% odds the sender is a 33-240 ohm unit, which is one of the more common types. If you put an ohmmeter across the sender terminal and ground, it should read somewhere between those numbers and move towards 33 ohms as it fills up.

[Al Schober]

I prefer doing some diagnostics before replacing parts.
Disconnect the lead at the sending unit. The gauge should move depending on whether the lead is contacting or not contacting the metal of the tank. That will verify that the gauge works and your wiring has connectivity.

[joe_db]

I prefer doing some diagnostics before replacing parts.
Disconnect the lead at the sending unit. The gauge should move depending on whether the lead is contacting or not contacting the metal of the tank. That will verify that the gauge works and your wiring has connectivity.

True if it just quit working, but that era C&C used gauges that don't last forever, my originals long since physically came apart or otherwise were obviously not going to ever work again.
Good point though, connect a 100 ohm resistor between the sender wire and ground and the gauge should read somewhere in the middle area. Also test the sender resistance to ground with the gauge wire off of it.