I can not get a 12vdc signal from the sub remote out wire blue with white stripe on a NESA 749nb, at one point I had power on the wire but when I got itr hooked up the power went away, I need a signal

If the head unit has any fuses go ahead and check those. Recheck all the wiring to make sure nothing was connected where it should't. If you still can't get any power out of the remote wire, there might be an internal issue with the head unit and if it's under warranty, take it back. The only other option is to use the red accessory power wire on the head unit and tap into that but the only thing is that when you turn off your radio, the amp will still stay on and will only turn off when your vehicle is turned off. I would prefer to have the head unit control the amp, so if it's warrantied take it back, but it's completely up to you.