Flickering Lights

After I installed my motor I developed a problem with my lights going dim and bright when I am driving at night. The car never used to do this even with 2 amps and a decent stereo. When I was driving the car in November I didnt have the stereo installed, and the lights would flicker at night. Can this be somehow related to the grounds? I doubt its the alternator because it was fine before I pulled the motor.

When I reinstalled the motor I didnt use the stock ground straps. I'm running a 4 gauge wire off the negative terminal to the engine block and then a 4 gauge wire from the engine block (on a different spot) to the chassis. I noticed the chassis ground started to corrode a bit because I ground it down to bare metal. I think that maybe I didnt make the contact service clean enough on the block. Would this cause anything to do with the lights? I dont have any problems with a dying battery or anything either, and the grounds on the lights are all fine.
 
If the lights are flickering off and on, it might have to do with you headlight switch or your multi-function switch. I had a similar problem and it turned out to be my multi-function switch. If they are just getting dim and not actually going off I would think it would have to do with the grounds. Check the headlight ground connections to see if they are clean of corrosion and paint.
 
If your stang has a fender-mount solenoid like an aero fox, ensure the connections are super tight and clean. That's where primary power to the circuits you mentioned comes from.

Good luck.