I have a 2012 Mitsubishi galant with about 188,000 miles on it and I am making it a custom car for the car show but here’s the problem when I put on the new headlights my underglow and headlights ran just fine but the taillights started acting weird the tail lights on the right side stopped working although I replaced the brake light bulb and my right side blinker light will stay on with the yellow color but when I press down to turn right the right blinker will still turn on properly but my left one will do the same except my whole tail light went out on the left side and it’s not a fuse the blinkers will also blink faster than normal what do I do? (My headlights aren’t led there just halogen headlights)

I don't think anyone here has much experience with aftermarket, underglow systems. Make sure all of your wiring is right. Electricity always follows the path of least resistance. You're not supposed be putting in all kinds of aftermarket glowing anyways, cars' electrical systems were designed to run as-is. Depending on your state, underglow may also be illegal.
@justin-shepherd Yeah, I really had no idea what he was talking about other than it sounds like he borked his car's electrical system with that garbage. Probably the thing to do is disconnect it all and return the car to stock and see if the problems go away.
In the mid-90s, customized cars had underglow, especially "ricer" Hondas, etc. and cops would routinely pull drivers over if they had them illuminated. I was only 7 at that time. They must have made a little bit of a comeback, because I've seen a few trucks equipped with aftermarket underglow systems in their wheel wells lately. I also think they're garbage. To each their own, I guess.