Audio Systems: power to car head unit/cd player, wirenuts, constant power

Question
hi. about a week ago i installed my jvc touch-screen cd player in my dad's car by myself. it looks like a normal cd player. no dvd or big screen or anything. it seemed to work fine as i played it for about 5 minutes. i turn off the cd player so i could wrap black tape around all the wires. and then i try to play it again and it all of a sudden doesn't work. i connected and disconnected the wires several times, for about 4 hours. and there still seemed to be no power going through. but i tested out the cd player with a power supply/battery and it still worked fine. so i checked all the fuses and they were fine also. i brang the car to a friend who used to work i the car audio business and he couldn't find out what was wrong either. so can you tell me what you think is the problem? thank you.

Answer
use a meter to verify the cars ground, constant power and switched power are all working,  if you need step by step on how to this please feel free to ask.
Use wirenuts instead of tape,  you can get a box of the orange ones at lowes or homedepot cheap.
Let me know what you find