Personally:
If this is at night and I am certain that there is someone breaking into MY car, I will (have wife) call the police, exit the house armed and be prepared, probably at low ready, certainly not from a concealed draw. When the threat level is assessed, I would make a verbal command to stop or get out of here, etc...
Depending on the outcome, I would act accordingly. While in Texas, it would be legal to use deadly force, I would not do so unless I was being attacked or the other person is armed and I can SEE the gun/knife, etc. Its just not worth it. The civil liability is more than I can afford to defend, so why bother.
Your results may vary, but remember, the jury is going to say:
"Was your car stereo worth killing this guy" (In my mind, yes, a BG is a BG)
Reality and the P/C world we live in will tell you no. Thats what car insurance is for.
Now...breaking into my home, armed BG or not, he is going down. I WILL shoot first and ask questions later in this case. Nobody is welcome in my home without an invitation. Under no circumstances would I waver in this fact.