I will assume it's the same as my 280SE 4.5:
The main box is under the steering wheel: Right next to the door light on the underside (It has an oval cover with 2 thumb screws holding it in).
There are also fuse boxes (radio, windows, etc) under the hood on the firewall.

__________________
Current:
2021 Charger Scat Pack Widebody "Sinabee"
2018 Durango R/T

Previous:
1972 280SE 4.5
2014 Jeep Grand Cherokee Limited "Hefe", 1992 Jeep Cherokee Laredo "Jeepy", 2006 Charger R/T "Hemi"
1999 Chrysler 300M - RIP @ 221k