Thank you for the added info...........
Factory AMP is located under the Rear Shelf, Driver side
IF Adapter Plug was used, then it is a basic "color for color" connection of the Plug to the Pioneer, including the BLUE or BLUE / WHITE wire to turn ON the AMP
Should have "some" draw for Memory of Radio, Computer, Modules, etc, less than 1 amp
Could be the Battery or cell is bad
IF you need further, let me know
Here is Battery Draw Test if you need:
Turn Ignition off
Roll driver window down
Close all doors
Using a "Multi Meter (VOM)
Remove the negative side battery cable from the negative battery terminal.
The meter needs to be able to read at least a 2 -5 amps for this test to work.
Attach a multimeter(set the dial on the multimeter to measure Amps as per multimeters instructions) between the negative cable and the negative battery post.
Wait a few seconds to several minutes for the car to go into sleep mode - i.e. when you make the contact with the ammeter, the cars computer systems "wake up". After a bit of time they will go back to "sleep".
If the ammeter is reading over 25-50 milliamps, something is using too much battery power.
Go to the fuse panel(s) and remove fuses, one at a time.
Pull the main fuses (higher amp ratings)last.
Perform the same steps for relays found in the fuse panel.
Sometimes relay contacts can fail to release causing a drain. Be sure to observe the ammeter after pulling each fuse or relay.
Watch for the ammeter to drop to acceptable drain.
The fuse that reduces the drain is the draw.
Consult the owners' manual or service manual to find what circuits are on that fuse.
Check each device (circuit) on that fuse.
Stop lamp, heater, etc. to find the drain.
Repeat steps to test your repair.
You can also try unhooking the big wire from your alternator.
The alternator can sometimes have a shorted diode that can cause amps to flow through the alternator's power cable and through the shorted diode and into the case and through the bolts and back to the negative battery terminal.
Make sure to read the ammeter before and after unplugging your Alternator