I'm not familiar with the Dodge Journey, but I ran into this same issue when I recently installed an aftermarket Alpine head unit in a Dodge Durango. Everything was connected correctly, and the deck powered up. But NO SOUND from ANY of the speakers! Turns out there was a factory amp hidden behind the front passenger's side kick plate. After much research and video watching I determined this was a VERY common problem for people who didn't know about the factory amp. All I had to do was bypass the factory amp, which was pretty simple. It was a friend's Durango, and he's going to have me install an aftermarket amp this summer, so he didn't care if the factory amp came out or was disconnected. I had to cut ALL the wires going IN and OUT of the amp and simply connect each one to each other, bypassing the amp. BAM, we had sound now!
Again, I'm not familiar with the Journey, but am wondering if you have a factory amp. If you simply cut the speaker wires from the harness behind the deck and connect speakers there, and it turns out you have a factory amp, you will NOT get sound! The wires from the stock deck would go to the factory amp FIRST, then to the speakers. This is the only reason I can think of why you would suddenly have no sound after you simply replaced a pair of speakers.
Another thing I learned from this nightmare Durango job was if you only want to replace ONE PAIR of speakers and leave the others connected to the factory amp (assuming you have one), all you have to do is run longer speaker wires from the head unit down to the factory amp, figure out which wires going IN to the amp and coming OUT of the amp are for the rear speakers, and cut them, then connect them to each other directly. ONE IMPORTANT NOTE: you always want to leave at least a few inches of wire from each harness when you cut them to leave plenty of room if you ever want to reconnect the rear speakers to the factory amp.
I've installed stereos for myself, for friends, and lots of strangers for over 40 years and this Durango was the FIRST vehicle I EVER had no sound from after I replaced a head unit, so I knew it wasn't me, it was something about the vehicle.
Please let me know if this helps any, and/or what you found out. I'm curious.