Here is the pdf. There is no mention of backlighting at all so it is safe to assume there isn't a dedicated wire for it. But, one would think that the backlight would come on with the on/off switch as it does with other versions. You might benefit from opening the siren up and seeing if there is a bulb inside. If it is an older style bulb (i.e. not LED), then the bulb may have burned out.
I didn't think so. I have 4 of these sitten here w/o backlighting. I had to hook up the hands free to the horn button so no one crashed trying to change the tones at night.