Starter not cranking the engine over?

If it is an aftermarket system then you may have tapped into a power wire you should have not to. To start with, if the clicking was fast and dash lights were flickering then you need to have the battery checked out first. Any parts store will most likely do it for you. If it was just one click then I would suspect a faulty starter but you need to verify the battery is healthy enough to support all the loads you have.

Sounds like a bad battery or the amp or capacitor is bad. 13.8 cannot be resting battery voltage, The best a battery can generate is around 12.6-12.8 volts. They have six cells that each make 2.1-2.14 volts.

Have the battery and alternator tested to be sure they are okay. If they test good then you can try connecting just the amp alone, then try just the cap alone. Whichever one causes the problem is the issue.

Thank you Steve. Was going to same something about the capacitor voltage since that is there to store voltage for the sound system and is not used to start the vehicle up.

As Steve suggested, have the battery tested. You may need to upgrade on your battery to a gel type battery.

How many amps? Voltage is useless without knowing how many amps it can supply. That is why you load test a battery and charging system.