Skunky280zx

New user here. I've got a lovely 83 280zx n/a 5 speed. I've been through all the electrical thread and there is nothing about the stereo. I need some clue as to what the wires are supposed to be for the factory radio. Previous Owner trashed the radio harness when he installed an aftermarket radio and amplifier. The power antenna works when power is supplied directly to it. Goes up and down just fine. But it doesn't do anything unless forced to by direct power. There are also several wires spliced behind the passenger seat and a blue/red wire is simply cut. I'm about to strip all the POs wiring out and try to start over due to being totally lost trying to figure out what has been done. Any help would be greatly appreciated.