Remote turn-on wit factory head unit and capacitor

I have a 1999 Ford Taurus.  Does anyone know of a source for the remote turn-on for an aftermarket amp from the factory head unit.  The car does have a factory amp in the trunk, but I don't have a wiring diagram to find the remote turn-on.  I am currently tapping into the factory radio fuse in the fuse panel to turn on my amp.  This works, but if I turn off my radio I get a loud humming noise from my sub.

I also have a second question regarding capacitors.  I am using a PPI 2360 running 360 watts mono to my sub.  The sound level tends to weaken as I drive my car.  I aked an employee at Circuit City about my problem as I was looking at the Monster Caps and he thought my problem was due to the high summer heat.  He said they were getting complaints from their customers regarding the same problem.  Is that correct or would a capacitor help me out?

There is a BLUE wire in the larger rectangular connection that is your factory remote turn on lead. As for the sound level lowering as you drive.... it sounds to me that road noise and wind noise adds to the levels in the car and this drowns out the volume of the stereo. That is why you must turn up the volume as you drive faster to compensate for the added noise of the moving vehicle.