So to not get confused your amp is staying on when the car is off? And the remote wire going to the amp is showing 0 volts when the car is off?(you have the test lead on the terminal at the amp?)
If this is the case then it sounds like the internals of your amp may be screwed cause the amp is not receving the signal to turn off when the remote wire turns off. The only suggestion I have is to get your hands on another amp and hook it up. If the new amp turns off then it is the internals(of the orignal amp) that are screwed, if not then something is screwy in your wiring. I know from experience that if an amp is going to die it is usually the remote lead internals which go first, all though usually it is the fact that the amp won't turn on at all but essentially it is the same problem. hope this helped without confusing you too much.
If this is the case then it sounds like the internals of your amp may be screwed cause the amp is not receving the signal to turn off when the remote wire turns off. The only suggestion I have is to get your hands on another amp and hook it up. If the new amp turns off then it is the internals(of the orignal amp) that are screwed, if not then something is screwy in your wiring. I know from experience that if an amp is going to die it is usually the remote lead internals which go first, all though usually it is the fact that the amp won't turn on at all but essentially it is the same problem. hope this helped without confusing you too much.