Ahh the Nissan POS 3-position temp gauge. It has been established that the 3 positions for the gauge are "OFF", "ON", and "Rebuild". I've made it to rebuild on my KA, but everything survived.

I've also done some research and found that FC RX7's have the same problem with their temp gauge, and that it's not linear. There is a fix somewhere for those cars to linearize the gauge reading that we may be able to adapt to our cars. If anyone finds the FC mod, I'd be glad to try it on an S13 gauge.