Firstly try to find the GND. It is usually the largest metal part on the PCB, e.g. that metal rim around the attaching hole is GND.
Next task is to find the power. Quite easy, becuse it is protected by a fuse on the PCB (small, smd fuse) marked as F1 on the PCB.
It is NOT neccessary to have only one gnd and power. Determine the twin wires by a multimeter with shortcircuit beeper function.
On newer backlight the power is usually works by 12V.
There is an enable line (ttl, so usually needs 5V) and a light control (give it 2.5V first, then you can increase or decrease). You can guess. Give the voltage to these remaining pins via a 100 Ohms resistor.
When there are no twin lines, try to determine, whether they are connected anywhere at all?