Low coolant alarm

[in2trux]

I'm about at wits end with this.
It gave me a problem a few months back. After removing the plug and cleaning it went away.

Since it came back I've replaced the sensor in the surge tank, the plug and pigtail, chased the wires back several feet inspecting for damage or fatigue, short of main harness that plugs into the ECM.

The old sensor only had two wires with one blank pin. The new sensor has three wires as well as the plug. I matched the wires to the old plug plus have tried every other combination.
My guess is this is this is part revision for later models.

My understanding is this is a 5 volt circuit but is showing 4.6 volts on Insite.
Coolant level is rock steady and never low.

Is there another sensor that could be causing this problem?
Any help or suggestions greatly appreciated.