Writing about a 2004 GT with about 20,000 miles on it. Went to the dealership for non - working AC/Heat blower fan. They replaced the harness, which was said to be water damaged, which took a couple of months. Drove it out started getting warnings like optical system bus not connected, brake light warning (which had to do with what seems like an unrelated failure of 3rd brake light.) and parking brake warning light. Back to dealer. This time while driving home the main screen rebooted but, no other warnings. Then the other driver of the car told me the screen rebooting was happening multiple times while driving. Fast forward to the last 2 weeks and now there's a traction control warning, check engine light, and the following problem.

To hopefully reset some of the issues, I disconnected the batteries for 3 days thinking I could get the system to reboot, reconnected batteries and when I first got it out of the garage, cold start, there were visible exhaust fumes rotten egg smell and car feels a little rough. Took it down to a friend mechanic, who told me "Yes, rotten egg smell is wrong." He then had me put my hand by the tail pipes. The passenger side was hot and strong, the driver side exhaust was cool and weaker. This was after driving 2 - 3 miles. Drove it back home, both sides exhaust hot but, that driver side still felt weaker turbulent, passenger side still felt normal. The check engine light is off (But car hasn't driven 50 miles yet) traction warning light came back on, parking brake light coming on intermittently, and brake light warning on (The 3rd brake light is completely out.)

I know I left a lot to unpack here but I appreciate anyone's opinion on what's going on and next steps. Thank you.

This 04 has a sagging headliner, 3rd brake light failure, needs upper control arms, and just today the ever - popular broken dipstick tip.