...I have the exact same problem with my 1993 corolla.......Brake System warning light and discharge warning light
Explanation of 2003 Toyota Corolla Dashboard
The dashboard symbols on the Toyota Corolla as well as other vehicles are designed to help you know that your car is running properly. You will find your engine light, oil gauge, hazard lights, and blinkers with your dashboard symbols.
Low tire
What model of Corolla ? You have to take the dash board out and the bulbs can be removed and replaced from the back. The dashboard on the Corolla is not that difficult to take out, but you have to do it slowly and carefully.
Turn the nob on the right side of the odometer.
Deep inside the dashboard behind the glove box
because you hooked into the lights ground I bet usually you blow the fuse everytime you turn on the lights check your radio ground
Try parking/tailight fuse
To remove the radio in a 1995 Toyota Corolla, first pry the radio frame from the dashboard using a flat tool like a screwdriver. Then, press in on the pins at each side of the radio and slide it out of the dashboard. Remove the wires from the back of the radio.
There's a perfect write up at http://www.toyotanation.com/forum/t139119.html !!! I had to replace a burnt dashboard light bulb.
Take it to auto zone and have the codes read for free.
Under the dashboard in the drivers footwell ... near the bonnet release catch.