I kindly need help fixing this
That’s an older remote starter or alarm system that’s been in place for some time. It’s likely that the zip tie securing it broke, or it came loose from where it was tucked away. Just get a new zip tie and fasten it back in place.
It definitely seems like an aftermarket security or remote start system.
I believe that’s actually the BCM. It has other functions as well, but it’s definitely a key component of the car. The starter and ignition wires are located there too. If you lie on your back on the floor and look under the dashboard, try lifting the box to check if it has a black plastic mount. The wires are the exact length needed, so it should easily fit into its correct position.
If all the glass is intact and the car was locked when you returned, it’s likely that no one tampered with it, and the zip ties on that module simply broke due to age.
Your car has just had a pro-lapse
Was your car unlocked?
This equipment is definitely aftermarket for a Nissan, as Nissan doesn’t utilize those Bosch-style relays. The bundle also includes speaker wire and vampire taps. If you have an alarm system, keyless entry fobs, or a remote start kit, and the fobs aren’t labeled Nissan, then this setup is likely for that. However, if you don’t have an alarm or remote start that you’re aware of, you may have a collection of outdated and unreliable wiring in your car. It might be a good idea to have a mechanic remove this confusing mess for you.
It’s probably an aftermarket remote start; either a zip tie has finally broken or someone tampered with it.
Someone tried to steal your car