In the illustration, the IVR gets power from the connection on the left.
View attachment 1716220336
When power is available, electrons move and we say current flows from the power supply to the ground.
Lets show the current from through the IFR.
Some electrons go through the resistance wire (heating element) to ground, and others continue to the gage and sender if they are connected.
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Its the heating element that needs the ground. For the rally IVR this ground is on the back of the gage as seen in the other thread.
When the bimetal gets hot enough it breaks the connection.
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Over time the input from the "12 volt system", really 14 V when running, results in output from the IVR that averages about 5 V over time.
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My apologies if going over the IVR seems extraneous. The point is the ground at the IVR is for the heating coil, and each of the senders gets grounded to complete their circuits. So flow is like this.
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from here
Thermal-Electric Gauges (Session 227) from the Master Technician's Service Conference
