PeterH:
BigMan73:
I noticed 2 months ago that when the temperature rises (I have an onboard I2C thermometer connected to Arduino) the reading of the gear voltage goes down.Have you measured whether the actual voltage signal received at the Arduino goes down? That would tell you whether the change was caused by some temperature-related inaccuracy within the Arduino's ADC, or something in the external circuit.
I measured the voltage of the motorcycle gear line, and it hasn't changed.
Should I measure the voltage between the analog port (e.g. A4) and GND?
I will do so.