The capacitor will not likely solve you dimming lights issue. I did nothing for mine. The Yellow top will help some, but what you really need to do is upgrade the alternator to a high output one. Ther are some after market manufacturers like Mean Green but the most economical approach is to buy a used one from a Nissan Quest from a junk yard. You could also buy a remanufacturered one from PepBoys or some other store like AutoZone, Advance Auto Parts, etc., someone on Ebay has a high output alternator listed for the Xterra also, I think it's 165A. Whatever path you choose you basically need more amps coming from the alternator to accomodate the draw from your amps. I personally am running an 800W Orion 8002 in bridged mono to a 15" Sub pulling the full 800W at 4 Ohms and an Orion 4004 running my mids/highs at 50W x 4 at 4 Ohms. I bought a used Quest alternator from a local junk yard for $40 and it eliminated my dimming light issue all together. A lot of car stereo buffs will also tell you to upgrade your battery cables to larger guage. Know as the big three: battery to alternator, battery to chassis and ground.