i have a pioneer head unit and replaced the stock speaker with 6" pioneer and the problem i have is that everytime i pump it up loud the head unit light start flashing. it also happen regardless if there is an amp or not..
thanks for any help

 

Sounds like a defective head unit. The only other thing i can thik of is that its drawing to much power from your batter. If that is the case your battery is probably see better days and needs to be replaced. Maybe somone else can think of another reason though.

 

Sounds like your battery, but you shouldn't need to upgrade it just to run a headunit and a couple of 6" ers. Probably slightly flat or, if your car is gettin' on, check for whining noises from your alternator.