Why doesn't the radio/uconnect/multimedia fuse blow? Did I short out the radio unit?

[windymtnman]

I have a 2015 Ram 2500 Bighorn. It has the 8.4 radio VP4 unit with navigation and back up camera. I somehow shorted this unit out, when messing with the backup camera. The entire unit just quit and wholly nonfunctional.
A new unit's MSRP cost is $2650.00. So, I bought a used unit online for about 25% of that. The seller seems reputable and guaranteed that this was a tested, fully functional unit that I bought from him.
So, I installed the replacement unit myself and was very careful to switch it out, getting the wiring harnesses where they belong. The used unit came with some specific instructions as to how to get the truck's electronics to interface with the replacement unit. I followed them, and when it was time to turn the truck and the unit on, NOTHING happened. It's the same as the failed unit, completely dead.
I called the Ram dealer, and they wonder if the wiring harness has a short in it?
My questions are, does anyone have any ideas as to what may be wrong, or what happened here that these units aren't working?
I checked the fuse that's not in the fuse box panel and it was good, but I put a new fuse in anyway. If I have an electrical short somewhere, why doesn't the fuse blow, instead of frying an expensive radio unit or something else? I'm stumped and not only inconvienced by it not working, but it's all expensive too.

 

[Jeepstr723]

Could be a bad ground wire. There are several ground wires behind the passenger side headlight. They ground to the frame. I found several that were broken beneathe the grommet that bolts to the frame. You actually have to closely inspect the wires entering the grommet.