You can track down the problem without the box layout as long as you know where the box(s) are. Still, a parts store service manual would be a big help.

As a troubleshooting step, find which circuit (or fuse) is causing the drain. With everything off, pull the negative battery cable and hook a test light between the battery post and terminal. Any meaningful drain will light the light at least a little. If there is no light or it is very dim, hook a multimeter between the post and cable. Set it on DC amps and check for current on the highest amp setting. Back down the amp setting until you can measure the drain.

It is normal to have some small drain. 20 mA is "good" 50 mA is on the high side. With your problem, it is probably quite a bit higher.

Next, pull fuses one at a time and check drain. When the drain drops you have found the problem circuit.