The backlight is only a long and tiny neon bulb. It's the inverter that powers up the backlight. The power goes from the motherboard to the inverter then to the backlight. I would try to replace the inverter first cause it's a cheap part that you can find for $20 on eBay. What is your iBook model ?
yes you're right. I once installed a G4 iBook 12" inverter in a G3 dual usb iBook and it worked perfectly. Be aware that it also could be a motherboard failure but I would try to swap the inverter first to troubleshoot the problem.