The amp was in my last car and I was running 2 15" alpine subs and it never don't it then now i'm only running 1 12" kenwood sub and the sub is brand new and I've checked all the wires and apart from the earth being a bit long but not no longer that 15" long I no it should realy be shorter than that but were the amp is it's as short as it can be so I think it might be a voltage drop, how can I prevent this from happaning?
The earth will be fine as long as it is thick enough, in some cases good results can be achieved by running an earth all the way back to your main battery up front. In other cases this is necessary for good operation.
What I am saying is, don't worry too much about length, as long as it is thick enough and a good contact.
You may not have a good earth, especially ( but not only) if it has been moved recently, it would be worth checking/rechecking you have a good earth.
To check the cables you would pretty much need to go over them with a magnifying glass as even a single strand of cable can cause problems but remain unseen. The ends of the cables are common troublespots.
Other than that...
to test voltage drop you would need some kind of voltmeter/multimeter, connected as close to the amps as possible. If volts are shown dropping under use of the system to much below 12v then the amps may be switching themselves off, if not then volt drop is unlikely the cause.
