ponyup96

I purchased a 96 3.8 Mustang and have some electrical problems I hope someone can help with. The following components do not work:
radio, tachometer, ac, left rear brake light, cooling fan, horn.
I have found that there is no voltage to the following fuses in the main fuse box under hood:
cooling fan fuse
audio fuse
The horn fuse has constant 12v, so when the fuse is installed, the horn blows continuously, so the fuse was removed.
When the 3rd taillight bulb is installed, it causes the battery to die, so it obviously has a short. I checked and there is no power coming to the left brake light.
The right brake light works and the headlights work.
I'm not sure how the power gets to the fuse box, but I think it must come direct from the battery to the engine bay fuse box. I don't see any breaks in the harness before the fuse box. I suspect a break and/or short somewhere in the harness, but since there is no power to some fuses in the fuse box, I suspect the problem is in the wiring before the fuse box.
Can anyone help with a wiring diagram and point me to some effective troubleshooting steps? Thanks