3 Wire Digital Scale Strain Gauge Weight Sensor
I'd bet that the wires are:


Red: power
Black: ground
White: signal


But it's hard to guess what the "power" voltage is. If you knew the power voltage, you could connect that voltage across the red and black wires, and check to see what signal comes out of the white wire.

If you can't figure out a way to determine the proper voltage, you could use an adjustable power supply. Start with a low voltage (3 V is probably safe), and then slowly raise the voltage while looking for a signal with an oscilloscope. There's a decent chance you'll go too high and burn the sensor, but it may be your only option.

Are there any identifying marks on the sensor? Did it come from a battery powered scale?