There is one such connector under the back of the gas tank on the throttle side of the bike. The connector is white (or was on my 2020) but wrapped in black tape and taped to another connector; all right by the frame. It has three or four brown wires going into it (depends on the year and model). It is only powered when the ECM is powered so once you tap the starter button (even if you don't start it). It goes cold about 2 minutes after the starter bump or 2 minutes after you shut off the bike.
To test, stick the positive probe of a voltmeter into the plug and the negative probe grounded (frame or batter negative terminal). It should read no voltage (or micro). Then bump the starter. Voltage should jump to low 13s. Watch the voltmeter. After two minutes (for the models that have the wifi. Might be less for models without wifi), the voltage will get cut and drop back to nothing. That is the plug to use.
It would likely handle the small draw for a temp gauge that does not have it's own battery (this is the hot side of the circuit you'll create so ground someplace else). There are two (or three depending on year) unoccupied slots in the plug. This plug is also the best place to push in the sensor wire of a relay for an accessory you power direct from the battery, like an LED light bar.
Cyclops makes a great relay for their LED lights. The relay's sensor wire pushes into into the YZ connector described above, main power comes off of battery, plus has another section to power an additional accessory. I could have wired up a relay myself, but by the time I gathered the parts and took the time, the $50 for the cyclops one worked out cheaper.
