I went and bought a brand new battery, brand new terminals and got the starter checked out. Everything is pretty much brand new, but when I go to start it/turn the key, the buzzer for the door open doesnt go of, none of the gauges light up and the aftermarket tach doesnt come on, almost like the cab is getting no power at all
The first thing I would do is invest in a voltmeter. You can get a cheap one at walmart or any auto parts store.
I would be checking the engine fuse and relay center. See if you have power to it, then go from there.
I've seen them have bad wiring under them more than once.