Okay, so this guy I have never met before dropped by my house to the other day to ask for some help on his system wiring. He told me straight up he didn't really have a clue, and wanted me to check over everything. Well, of course, he had the ol' self tapper for a ground, and the power/ground inputs on the amp were Y'd and wrapped around the screw, and simple noobie mistakes like that. So, me being so helpful, fixed all his wiring...put some o-rings on his ground wire and found a suitable ground, put some spade connectors on his amp inputs, and put them in correctly. BUT, his amp would not power on, so I grabbed the trusty DMM. With the car running, his remote wire was seeing about 13.5v. But his main power input at the amp was only showing about 1.6v. So I went under the hood, and started checking there. I used the battery ground, and tapped my DMM power directly into the main power wire at the battery, and it said 13.5v. When i checked the power on the battery side of the inline fuse, it was still 13.5v. But when I went to the amp side of his inline, it dropped to 1.6v. Thinking the fuse had went chuck norris on me, i changed it...and this particular fuse holder used the blade type fuses. But to no avail, I still had 1.6v. He had a spare inline fuse, with a completely different fuse in it, not blown. This was the kind that uses a glass fuse. So I completely changed out the inline, and this still didn't fix the problem. So now I'm getting frustrated. I actually take a working fuse holder and fuse from my ride, and install it on his...but it was still showing 1.6v. I have no idea what the problem could be. I had assumed maybe he had a short between his fuse and his amp, but upon visual inspection, i coudln't see any burn marks, or burnt insulation on the wire. And the guy told me he had not smelled any kind of smoke or burning smells at all. Hopefully someone knows something about this without me having to completely run another power wire for this guy.
EDIT: I kinda feel like it is my fault it stopped working, because before I started wiring, the amp was actually working. When he would turn the system up, the amp would completely shut off, but that was due to his faulty ground. So I assumed by cleaning up his ground and amp inputs, it would solve the issue...but now it will not turn on at all. The only time I touched the power wire was when I put a spade connector on it so that it could properly fit in his amp input...but when I did this, I had removed the fuse, so it had no power, therefore was unable to short out while I was working on it.