Using a multimeter with a diode drop function (triangle with a line next to it), you can work out the pinout of an unknown Hall Effect sensor. This is a super simple schematic of what we're looking for (voltage can only go in the direction of the arrow):

Put the positive probe onto a wire, and check for a circuit to each other wire. When you find the wire that gives a circuit to both other wires, you're on the sensors' power wire.

Put the positive probe onto one of the remaining two wires. If you get a circuit to the other wire, you're on the sensors' ground pin.

The remaining wire is therefore the sensors' signal wire.