Farfar

Hello,
I just bought an Rx-8, literally 12 hours ago and i love it! Unfortunately, when i bought it, it was day time, so it never occurred to me that i should test the illumination lights until later in the day when i have already purchased my car. Turns out, my interior does not illuminate when i turn the headlights on. I tried adjusting the dimmer, but it doesn't work. To make matters worse, my DSC button doesn't work and constantly says DSC OFF on my instrument panel. I tried resetting it, but it still stays on. My check engine light and battery light is on as well when the key is in the ON position (Engine not ignited). I read somewhere that this might have been a TNS Relay (both of those buttons are apparently connected to it), so I tried taking out the relay and cleaning it, and i also let my ECU reset (I removed the negative part of the battery) but that didnt work either. I ALSO did see some oxidation (very little) on the negative side of the battery when i removed the battery cover (feel stupid not noticing this before i bought the car), would that mean anything with this problem? And what else should I do? The radio is the factory radio, so unless the previous owner had an aftermarket radio and swapped the radio back in before selling it, i don't see why the dimmer might have disconnected from the radio unit.
Besides this little problem, my Rx8 is perfect! but I have OCD and this will REALLY bother me until it is fixed,
Thanks!