Dear Friend
That is not correct, that auxiliary fuse box is intended ONLY for the side markers on an US spec car. Those are the white/green leads. Front and rear side markers are fused in that same position.
The radio if installed is fed through red/green switched T15 lead which can be found generally on the right fender main wiring harness loom taped. Think it is always close to the CSV terminal. Another possibility is close to the wiper motor, branch. So the radio should be fed through an auxiliary fuse box installed there. This comment is valid for 230SL and 250SL
I remember you mention somewhere in your post you have a late production 280SL. Well in that particular car, the cables arrangement for the radio may be completely different as your car came equipped with the latest 8 pin ignition tumbler switch which uses a round plug connector to drive signals to main harness.
That 8 pin round connector has a direct RADIO output terminal, so it may be possible to take power for the radio directly from there and have the fuse box behind the radio itself.
Nevertheless on the latest 280SL harness refurbished by me I have not found a red/green cable for radio connection anywhere in the engine bay part of the main harness as is normal on 230/250SL.
Hazard lights relay should be run from internal main fuse box, circuit no. 1 for the T30 lead and circuit no.5 for the T15 lead.
Globe box light circuit also belongs to main fuse box, circuit no.1
Hope this info helped you somehow in what to do with your electric system.
Best regards
L.Peterssen