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My friend re-wired his amp and we built a new sub enclosure for his volvo. Now, when going over bumps the car shuts off for about a second at a time, but then it kicks back on. Does anyone know what this problem could be? Maybe alternator, new battery? Could the ground wire for the amp be affecting this? Thanks.

(We charged the battery, wiggled the postive and negative terminals and it still didn't work.)

I was gonna say a loose battery connection. I have seen a car with battery terminals that were distorted from being tightened too much, so they would feel tight unless wiggled just right.