I decided to add a temperature gauge to my engine and keep the sensor for the warning signal as well. I have a Yanmar 2QM15 diesel but I imagine the setup will work for most engines.

Typical Warning Sensor

The folks at Mac Boring explained how I should do it. This photo shows a 3/8 nipple that is screwed into the engine block where the original sensor was. A 3/8 tee is screwed to the nipple followed by two sensors. In this case I used the original sensor for the warning signal and a new one for the gauge.

Dual sensors.

This shows the installation at the block completed.

I didnt include photos of the gauge. It is a standard temperature gauge wired according to the instructions that come with it. One wire goes to the ignition switch, one to ground and one to the sensor.

As for the warning signal, I just plugged the existing wire back on the sensor.

Installed