i have a soundstream pcx 2000d i have big 3 done but i get major voltage drops to almost 10v and brake lights dim also interior. i found a guy whos selling a tsunami 20 farad cap would this help the dimming and keep my voltage stedy or should i just invest in a second batt. thanks.

 

I'd invest in a more powerful alternator before either of those options. Then the 2nd battery.