When braking the car loses electrical power

Hey all. Almost two months back now, I got the car listed above (GL model) off Facebook Marketplace. Runs great, no immediate issues, and only had small fixes. I’ve fixed a few things, like the brake lights staying in and stuff, but I’ve started running into an issue. I’m not sure how long after I start driving, but I have noticed that when I start pushing down in the brakes to slow down before a turn, all of my power starts to drain. Everything starts to dim and chug along until I start accelerating again. I recently found a wire bypassing the cabin fuse box linking the stoplight switch to the engine fuse box. I cut it, thinking this would solve the issue, but I’m still draining power. Based off the appearance under my dash, it looks to me that the entire wiring system was rebuilt. I’m hoping to get a wiring diagram to try taking a look at what’s under my dash and see if something was done wrong. Any help is greatly appreciated!