Why is my Stereo not powering up in my car?

Yesterday I rewired everything completely and it was working fine. I attempted to try a different stereo in my car today so I exchanged them rewired again perfectly and it worked fine. After a few hours I realized this stereo didn't suit me too well so I changed back to my other. I wired everything like I normally would each being bonded together very tight. I ran out of electrical tape so I pushed the stereo in the dash for 1 minutes ran inside the house to grab some tape. I came back and my stereo would not power up. I have LED lights in my car which are connected to the black wire and the red wire and they power up fine. This tells me those two wires are not the problem. What's left is a blue wire and yellow wire. I tried rewiring them both multiple times but still no luck. What could have went wrong?