Hello 240dnewbie
You need an AMP meter.
Make sure that all lights are off, remove trunk light bulbs rather than guess.
Disconnect the negative terminal on battery.
Connect the amp meter from the negative terminal on battery to negative cable.
Watch the meter for 90 seconds, (some after market accessories take that long to return to rest state).
There should be minimal 1 amp or less or no draw.

Post the reading you get, we can probably guess what is wrong from the amp draw amount.
Have a great day.

__________________
ASE Master Mechanic
https://whunter.carrd.co/

Prototype R&D/testing:
Thermal & Aerodynamic System Engineering (TASE) Senior vehicle instrumentation technician.
Noise Vibration and Harshness (NVH).
Dynamometer.
Heat exchanger durability.
HV-A/C Climate Control.
Vehicle build.
Fleet Durability
Technical Quality Auditor.
Automotive Technical Writer

1985 300SD
1983 300D
2003 Volvo V70

https://www.boldegoist.com/