After we got the POS Mazda home, I tried to start it, wouldn't start. Popped the hood and notice a loose wire, couldn't figure out where it came from. I checked on my truck, and found that it was supposed to be connected to the master cylinder. Just wondering if the loose connection could have caused the rear brakes to lock up. Any help is greatly appreciated. I have to find out what caused this crash.

As far as I know, the only things that should be connected directly to the master cylinder are the brake lines & the brake booster. Unless you have a fluid level bob or something connected to the top of the master cylinder.

You might want to see if its supposed to connect to the ABS module (if equipt). If you have ABS, and something happened to it, then its possible, but extremely unlikely for it to lock up. Very, very rarely will an able prob cause a physical prob. Normally what will happen is that something inside the system will fail, and the computer will deactivate the ABS system. The vehicle will have normal braking capabilities, but not ABS, this leading to the possiblity of brake lock up. But in that situation, the ABS light should be on, indicating that some sort of problem or failure exists.

The truck should have a level sensor at the MC. If this was disconnected it may cause the RABS system to detect a fault and disable it, the RABS light would have come on. Without RABS you would be surprised how easy the rear brakes would lock since there is very little weight on the rear end and the back end would want to pass the front. Hope this helps, I'm not sure what the whole story is with your truck.