well.. your lights dimming might not mean you need a cap. What size wires you using?? From the batt to the amps. If its not big enough, having a cap wont help either. I remembered that on my old setup, I was using 8 gauge wires for running 2 amps. my lights dimmed like hell. But now that I changed over to 1 gauge wires.. its just fine. I also added in 2 caps just for looks really. Cuase im not about to run the risk of shattering my rear hatch.. Dont think thats really pussible.. but Im always scared of that.