When an amplifier causes trouble or otherwise stops working, it is necessary to eliminate external possibilities such as a short circuited output.
If nothing external is causing the problem, unless you have a good friend who is an electronics engineer, it will be a repair shop task...
Double check your connections. Sounds like you are picking up alternator whine. Make sure the rca cable is at least 12" away from power and remote cables when installing fem radio towards amp. Its best to runthem on opposite sides.
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The spark is normal since at the initial time of the connection, the capacitor has 'zero' ohms. As it charges, less and less current flows until it is fully charged. The only way to 'pre-charge' a capacitor is to connect it to power. You can put a resistor in series and slow the charging rate and thus the spark will decrease/go away. Pick a high ohm maybe 1watt resistor, put it in series and go for it.
You must be deaf!
It is rated at 5kW Total Music Power which is about 1250W RMS.
How many alternators have you got running to cope with the power required at full power (90Amps) and have you run 16mm cables to your speakers and 20mm from the battery?