to power my amp I ran a cable from battery to boot.
Switched ignition live. easy. Turns on and off with ignition.
If it's not powering then obviously you have no power... so it's a wiring fault. Take power from battery but use the switched live to turn it on/off etc.
I'm sh*t with wiring, I get my mate jairm to do it for me. im fine with mechanical stuff but electricity is like women, cannot be comprehended.