I have a digital 3.0ferad capacitor and when i shut the car down it continues to display 13.26 and it stays lit up. is this normal?

 

That's a large cap. Yeah it will always show what the voltage reading is. It's always connected to the battery.

 

Hooking it to the battery was a little scary.... there was a huge spark. but as soon as it was connected it was fine.

 

There should have been a charge/discharge plate that came with it. I know Rockford Fosgates come with them and prevent the spark. I had a breaker 60 amp breaker on my power cable, so I tripped the breaker, wired in the cap, and then reset the breaker to avoid the spark.