98 camry power window, mileage gauge, gear shift light on dash, aren't working

I would undo what ever you did and put it back the way it was. Then buy the brake light relay. I don't know what you cross wired to bypass the brakes, but you may have toasted half of your electrical system. You may have fried half of your computer. That's a lot of electrical failures to happen all at once. You can start by checking every fuse under the hood and in the car. The windows should be on a relay. Hopefully, you just blew some fuses. If not, you have a lot of work ahead of you.