Date:         Fri, 30 Sep 2022 13:59:48 +0000
Reply-To:     Dennis Haynes <d23haynes57@HOTMAIL.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Dennis Haynes <d23haynes57@HOTMAIL.COM>
Subject:      Coolant light mysteries continued!
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For diagnosing the coolant light we need to follow a process. Then need is to isolate the source of the problem, wiring, the gauge, and the coolant level module, controller, whatever you want to call it. To do this we need to know the function of each part and the process.

The gauge and included light. The gauge itself get power from the gauge source voltage regulator. This powers both the temp and fuel gauges. There is a ground connection through the foil and other connections, and there is the wire to the temp sensor, also connected to the coolant level sensor controller.

The logic to turn on or blink the warning light is strictly within the gauge itself. Upon power up it should blink for short time to indicate that it is working. As the coolant heats up the resistance of the temp sensor goes down causing the heater in the gauge needle to raise the needle. At some low enough resistance the circuitry in the gauge turns the light on (blinks) to get your attention.
Should the coolant level go low the low coolant controller will connect the temp sensor lead to ground, causing the gauge to rise and turn on the warning light. Based on year or replacement parts there are two controllers in use. The early units would just connect the sensor lead to ground causing the gauge needle to fully rise and the light to turn on. The later units pulse the sensor lead connection which does not allow enough time for the needle to rise but still turns on the warning light.

So the first step to diagnose is to unplug the low coolant level controller. Does the gauge and indicator light now reliably work? If yes, not test the controller. If not now you just have the gauge and wiring up front to confirm. The circuits in the gauge do fail. Some have fixed replacing the timing cap. Sometimes you need to find another one.

Next would be the controller and sensor. For the wiring the wire connections on the level sensor plug and connector itself are suspect. One of those wires goes to ground. Check that end also. And yes those controller often go wonky. They can also be effected by electrical noise. I have relocated some to the engine compartment stuffing them in that junction box left front of the engine compartment.

Dennis