If you review Step 5 in this [guide|30260] we can see the two power feeds from the backlight bars are feed from a single cable from the logic board. I would remount the controller so you have a single cable connection and then viewing the iMac’s logic board schematics we can then ID the pinouts and the voltages going to the panel. As far as the LCD driver logic I can’t tell you how to de-energize that part but I don’t think that stops your use.