I really don't know what tell with out looking at it obviously.
The lights brightness and dim has to be a separate issue. Something electrical is what I'm leaning towards. I had a similar problem. Every time I turned the radio on it would go crazy. I checked all the fuses and relays, found a couple of burnt fuses and changed it.
First thing you can do is to reset the ECU. disconnect the battery for 5 mins and connect it again. That will reset the ECU. Check all the fuses and stuff. Replace any burnt fuses. This might not be ECU related at all. Bad O2 sensors also trigger the check engine light. If you know some one who have a similar car, try his ECU in your car. That way you'll know if it's the ECU or not.