97 ford taurus head light dimming problem

Ok this is what is going on. My brother has a 97 ford taurus and he has a dimming head lights problem. He has a 140amp alt,replaced all the switches (headlight,dimer) He has 2-12"s with 2 battery's and a 5 farad cap. The thing is before he put the system in it was dimming and that is the reason he replaced the switches. If anyone know something that we can try let me know. thanksRonald Bailey Owner/ Installer of VIBRATION CUSTUM SOUNDS. CUSTOM BOX DESIGNER AND BUILDER

TID-896 7" screen,Amp-BX1206d

4/0power/ground cables

4-12 mofos 12ft3 box tuned 40hz DB:163.1

Sorry forgot to say that in my post. We did the big three first then everything else, that is why we thought it was the switches. Thanks for the reply.Ronald Bailey Owner/ Installer of VIBRATION CUSTUM SOUNDS. CUSTOM BOX DESIGNER AND BUILDER

TID-896 7" screen,Amp-BX1206d

4/0power/ground cables

4-12 mofos 12ft3 box tuned 40hz DB:163.1

I would hook the headlights right to the battery using a relay pin 85 would go to ground, pin 86 would goto the RED / yellow wire at the switch, pin 30 would go to the battery, fused of course and pin 87 would go to your headlights