Wow, we be all over the map here! LOL
You have the amplifier in the car, and there are three power lines going in - one for hot (red I hope), one for ground (black I hope), and one fore remote (blue I hope). I like to follow convention if its not obvious. //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif
My understanding of the above is that with the amplifier installed, you see 2V between the red and black wire? If that is the case, as already stated, something is bad in Denmark. Or Piscataway as the case may be. That should read battery voltage. If it does not, it is because something is on fire (I'd think that oyu'd report that), or because the main fuse is bad, and you are reading back-fed voltage (which means something else is bad).
What they want you to do is to slide the red wire out (do NOT let it touch anything), and then read the voltage from the end of the now-exposed red wire and the black wire in the amp. Is it still 2V, or do we have 12V now?
Next, test using a known good ground (body panel somewhere with a clean exposed bolt. Put the black lead from the multimeter on the bolt, and the red lead on the end of the red wire. Still 2V? Or maybe now 12V? Or maybe millivolts?
If 12V, you have a bad ground.
If millivolts, you have a bad fuse in line with the main power lead (yes, you checked them, that's greaaat). ;-)
Report back.