A couple of tips when removing Tach/Speed round gauges on the RF18.
1. remove water supply tube from Speed gauge. Pinch tube with hemostats if you're going to run engine.
2. Carefully disconnect two harness plugs on Tach. The plastic pins bend away from connector with small blade screwdriver.
3. Loosen four bracket 7mm bolts, lock washers. I did mine with pliers. Pull out Tach gauge. Label each connector with correct color male lug wire pin. Remove gauge.
4. Repeat for Speed gauge.
For reinstalling gauges reverse the process. Connect water supply tube after wires are connected. If not you will have trouble fitting bracket.
I coated all connectors with dialectric grease.