Electrical issues Burban dies and won't start

[zombiescustoms]

I have worked on a lot of vehicles in my day and have never seen this: 1989 Suburban 2500 2wd, 454ci, started having problem the other day, statrs fine, but when you hit the brakes it dies, and the volt gauge showes no voltage, it will start right up though and run fine the reas of the day, today it does the same thing but this time it stays dead, so I think it must be the trailer brake controller the PO installed, so I disconnect the circuit braker and all the other wires going to the box, truck starts, hit the brakes and it dies again, so then I disconnect the brake light switch, nothing, whats weard is the lights all work, clock works etc but other gauges are dead and windows don't work, I think it may be a ignition switch, but why does hitting the brakes cause it to die?? by the way it has all new bat. cables new battery, new alt. all fuses are good, could it also be a fusable link on the power dist block on the firewall?? Help please as right now I'm stranded at work!!