Originally Posted by projectRDM

Um, this thread is full of wrong. The red/yellow wire in question is the dimmer lead to the OE radio, you do NOT ground it unless you no longer need a dimmer. The red/blue is the illumination wire, sounds like the OP either blew a fuse or the dimmer went bad, the correct fix is not to just ground the dimmer lead though, that's fucking stupid.

To the S14 guy, check fuses. Simple as that, when a radio is pulled and someone cuts all the wiring you usually ground something out on accident. If ALL fuses are good, the dimmer switch could be bad. The red/blue wire behind the radio should have +12V when the lights are on, the red/yellow should show a ground, but it's a variable ground through the dimmer. Grounding it negates the dimmer completely.