Why is my guitar amp cutting in and out?
It is either your power cord has gone bad, or the jack for that power cord gone bad. Or both. Either way, try to change your power chord and see if there's a significant difference. Or try this: wiggle your power chord when your amp is turned on, with guitar plugged in.
Why does my amp turn off when I turn up the volume?
If the car stereo or amplifier powers off when raising the volume, then there may be an issue with installation. This usually occurs when the ground wire is not connected properly. However, it also can occur when an amplifier becomes overloaded by connecting too many speakers.