On the Rywire engine harness, there is a connector labeled H20. This normally connects to the gauge cluster temp sensor located on the upper water neck on the Honda K20.

The Hybrid Racing conversion harness has a wire labeled "coolant temp." In order to control the gauge cluster in the EG/DC/EK chassis, you'll need to connect the wire labeled "coolant temp" to pin 6 on the Rywire engine harness.