RC Joystick Question: What is this component?
The component is a simple jumper (notice the letter J), it's there so those "contacts" can make contact when you turn it. like a switch.

Three wires are; two positive and one negative. so when it turns it pulls down probably an MCU pin to ground when you turn it.

I think you're measuring wrong with you're multimeter, measuring the polarity reversed so it shows you negative voltage. If you're sure of measuring the voltage correctly, you have to show us the whole circuit/schematic to be able to say how -3 V is generated.