The amp turn on lead should be 12V but with very little current. The bad thing is that with some amps if the ground on your amp was not good the amp may seek ground from the first place it could find, wich would be the patch cable ground wich then could damage the sig. ground out in the empeg. The first thing I would do though is find out why you don't have 12v at the power leads on the amp and then go from there.