Yup, as was already stated, here is the standard diag route for finding dimming light problems:
- Check amp power wire, it is sized accordingly?
- Check amp power wire fuse, is it sized accordingly?
- Check ground wire on amp, is the paint scuffed around the ground, is the ground sized accordingly?
- Check Battery Voltage (make sure it reads 12v AT LEAST).
- Check speaker wiring (make sure the amp isn't downloaded when it doesn't handle it)
- Test battery w/ multimeter during high load (make sure voltage stays above 12v)
- Take car and test alternator (they can also test battery)
Any of these can cause your lights to dim. If you're still having problems and nothing here solves it, then your alt is probably not powerful enough. (I've noticed lights dimming in stock cougars w/ accessories turned on, such as rear defrost, headlights, turn signals, etc.)
E1