Has anyone experienced this?

My headlights went out, but high beams still worked. They replaced spark plugs and battery. But then headlights went out again. To pass inspection the guy wired a line directly from my batttery to my headlights so they would work. Then said i'd need to take it to Chevy to fix otherwise. From him doing this my headlights have now blown out again and now my intrument panal is going crazy, if im driving 25 mph, it reads as 75 mph, seems like everything is way over what it should read in general.

They had suggested there was an electrical relay problem because the fuse wasn't blown in the past. But I am wondering was it just the alternator this whole time that needed to be replaced and now is my instrument panal fried because they wired a line from the battery to the headlights because that's when it started acting weird the panal after the lights blew out.

Is there any history with 2004 trailblazers with electrical relay issues? Or know what is causing this? I don't want to take it chevy I'd rather a local mechanic fix it for cheaper if I could.

Thanks!