Aftermarket Temperature Gauge, with +ground??

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Has anyone successfully fitted an aftermarket water temperature gauge to their +ground Amphicar? I purchased a nice VDO gauge, which I intend to tastefully install under the instrument panel to replace the function of the tiny original gauge in the instrument cluster.

I’ve been testing the new VDO gauge with a battery, placing the sensor in hot water. Set up as negative ground, it works properly. It has three terminals: +12V, -ground, and the sender, which goes to ground when the temperature rises (rising temp is less resistance at the sender).

The VDO tech told me to just reverse the +12 and – ground terminals. It appears that would work, but sweep of the needle must be polarity sensitive – the needle goes the wrong direction.

Any suggestions on how to wire this gauge?

How to rewire the gauge inside?

Another brand gauge you’d recommend?

Note: I don’t want to convert the car from positive to negative ground.

Thanks, Doug
Update - I finally found a tech at VDO that confirms their temperature gauge will not work with a positive ground car. I found a positive ground temperature gauge at a company called Westach ( They will custom make a + ground gauge, with a special two-wire sender. The gauge looks somewhat period-correct for the Amphicar.