Where on the engine block would I put a thermometer for a quadbike?

I have a Honda 350D and the fan thermostat has broken, rather than spending money replacing the unit I'm looking to wire the fan into a switch.

I have also purchased a digital thermometer which I plan to wire in, but I need to place the receiver on the engine block, but which part do I connect it to, top end, or radiator and if so top of the radiator or bottom? (oil cooled).

Many thanks in advance!

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