1) The brake light failure light keeps coming on from time to time. It's the eye light. I've replaced the bulb, and tried to adjust it, but to no success. Any suggestions?
Ans> did you happen to replace or check the brake wear sensor.

2) After turning off the engine (every time I drive the car), the computer reads to check coolant levels. I've had a coolant flush, and replaced the sensor. The levels are fine, what is the problem? Is the sensor detecting an internal leak?
Ans.> An internal leak would surely lead to you spotting collant in your driveway. Did you check your collant level in the morning (or when engine is cold)and the coolant level should be no more or less than the Kalt/cold mark.
3) The left rear speaker is not working due to wiring and not the speaker, how do I replace the wiring? Doesn't it run through the interior of the car? (I switched speakers and the speaker worked fine, its just the left rear wiring.)