my car for some reason, for the first time ever has the high beams come on ONLY when the lights are turned off completely, doesn't matter if my car is on or off -- which is the key part, because my car is now turned off, but my high beams won't come off and it's now draining my battery.

It's a 97 mustang, and i've tinkered with the high beam switch/etc and taken the car for a drive, etc. and nothing has fixed it. I tried looking for a fuse for it in the owner's manual but nothing was mentioned as far as fuses for high beams.

I also tried applying the parking brake (its an auto) and that did nothing.

 

It could be possible your multifunction switch is not good anymore.

 

I don't think its a fuse, because when they go bad they make electronics stop working, not start.

This is where it pays to have the factory service manual and electrical diagnostic manual.

According to my '98 Eletrical, Vaccuum Diagnostics Service Manual, the power for the high beams goes through the multi-function lever thing in the steering column (the one you can pull in towards the steering wheel to momentarily put the headlights in high). If you disconnect the wiring for that lever, do the high beams turn off? If so, one of the switches inside the lever is bad and you have to replace the entire lever. If the high beams don't turn off, check light green and black wire in the connector that the lever plugged into with a volt meter to see if it has power (it shouldn't). If it does, then you have a short somewhere between the steering column and the head lamps. The light green and black wire goes all the way to the head lights (with a couple connections in between) without changing colors etc. So just trace it down the line until you find the short.

Good luck...