I guess I misunderstood. I thought the backlight was previously lighting up.
It could be that backlight is burned or perhaps the glcd does have an EL backlight.
If so, to make it work you need high voltage high frequency to drive it.
You can buy EL power inverters for as low as around $5 USD.
What about the contrast control. Is that working?
Is the multimeter digital?
If it is connect the meter black/- wire to gnd, then connect the Red/+ wire
to pin 3 of the glcd.
The voltage you see should be negative.
Do you see the voltage change when you rotate the contrast pot?
At one end it should be like negative 7-10 volts and as you turn the pot the voltage should
rise up to zero at the other end.
--- bill