Hi, I have a 2000 v6 Mustang. I hate to have to ask for help but I just spent 800 on fixing this car and can't afford to bring it in again.

So I am having a very odd issue and am not sure where to start. The gauges on the dash don't work and when I turn on the headlights the gauges all jump as if I started the car and than go back to not working. Also if the headlights or heat is on the blinkers will not work. Also, when the headlights are off the check engine light is on along with the theft light but with the on they go away... I am thinking its a ground issue but I don't know where the grounds are and the fuses seem ok. Any advice would be great!